Earth's great rivers...
..make extraordinary journeys.
Carving through continents...
..feeding and connecting life...
..nurturing culture...
..providing a place for adventure.
From the frozen wilderness of the Yukon...
..to the tropical heat of the Zambezi...
..and the magical, hidden worlds of the Danube...
..great rivers are the lifeblood of Planet Earth.
In the heart of Africa
is a forest.
A sacred place.
The Lunda people call it "yambeshi"...
..the heart of everything.
Here, a clear spring
bubbles to the surface.
The source of a great river.
One day, hippos will wallow in its deep, dark pools...
..and elephants will wrestle with its treacherous currents.
It will carve its way through bedrock...
..and its waters will fill great lakes...
..and spread out to form the largest curtain of water on Earth.
For this trickle to become one of Africa's mightiest rivers,
it will need to overcome many obstacles...
..on its epic journey
to the Indian Ocean.
But everywhere it touches,
it will bring life.
This is the story of the Zambezi...
..Africa's wildest river.
From its source in the northwest of Zambia, the Zambezi travels
over one and a half thousand miles,
through six countries, on its course
to the Indian Ocean.
Like many great rivers, its beginnings are humble.
And its destiny by no means certain.
Flowing down out of the forests of its birth, the Zambezi
starts its great journey.
But just as its waters are getting going, it runs into trouble.
Barotseland.
An endless flat plane in the far west of Zambia.
So flat, the Zambezi completely loses momentum.
And it's September, the peak of the dry season.
Its waters are evaporating under the heat of the African sun.
But it's just now that the Zambezi is vitally important.
Especially for the people that live here,
like cattle farmer Makalo Makaulo.
September is the hottest time in the year,
where everything is dried out.
I tell you we are suffering because we depend on water.
Here in Barotseland,
everything depends on water.
Every day in the dry season
to keep his cows alive,
Makalo Makaulo must take them from the arid grasslands
to the Zambezi's life-giving waters.
Zambezi River,
it's like a father to me.
The father who feeds his children.
The parent of Barotseland is Zambezi.
But as the heat intensifies,
the Zambezi's waters are receding...
..leaving miles of dry, hot riverbed.
A challenging place,
whatever your walk of life.
But there are advantages to the dry season.
For schoolboys and cattle farmers alike,
life goes on through the dry season.
As it does for the wildlife here.
These vast plains are home to some of the greatest concentrations
of wildlife anywhere in Africa.
And this is their toughest time.
But the heat can only build for so long.
It's now October, and a change is coming to Barotseland.
Over 30,000 wildebeest are on the move.
They are heading for their calving grounds in the south of the plains,
in anticipation of the rains.
A sign that six months of drought is coming to an end.
When the rain is coming,
everything is changing.
In October every year
tropical rains push down from the equator, and spill
over into Barotseland.
This is what all the inhabitants have been waiting for.
So when the rains come, our hearts are feeling very happy,
because we are expecting good things to come.
I don't know how you even express it, because everything there, even
the nature of the land is changing.
The rains are completely transformative.
A greening of the land over 7,000 square miles...
..that can even be seen from space.
My God, why can't this period be like that always?
As the grasslands are revitalized,
they become a globally important wetland,
supporting 350 species of birds.
And finally,
the wildebeest arrive at their calving grounds.
Over just a couple of weeks,
all the herd's calves are born
to coincide with this time of plenty.
CROAKING
But the rains are having an even more dramatic effect...
..on the Zambezi.
It starts to flood.
The people of Barotseland have always lived in tune
with the annual flooding of the Zambezi.
Larger villages are built on high ground,
so they stay dry during the flood.
But many smaller buildings
are designed to be submerged for a while.
Abandoned for four or five months until the waters subside.
The rising waters bring new challenges.
Most children have to stop going to school in the wet season.
But this school has been built with flooding in mind.
Set on a mound of high ground,
it even has docks for the pupils to tie up to.
So long as they can brave the school run,
Gift and his classmates can keep
learning while the waters keep rising.
Cattle farmers don't have the option of staying in the floodplains.
They now take to canoes to swim their cattle
to higher ground.
But beneath the waters,
the land is being fertilised
by the Zambezi's silt.
So when the cattle return,
they will have some of the most
nutritious grass around.
The floods are not only good for the inhabitants
of Barotseland...
..the waters of the entire flood plain are now gathering
into one rejuvenated flow.
The Zambezi
is on the move again.
Heading out of Barotseland,
the Zambezi now turns east
where, for the next 300 miles, it will form the border
between Zambia and Zimbabwe.
Boosted by the water from upstream,
the Zambezi grows.
And, as it grows, it brings more opportunity for life.
The Zambezi is starting to look like a great African river.
As it flows over a series of steps in the bedrock,
it starts to gather pace.
And, in the distance, a cloud of mist is rising.
A hint of what is to come.
Right at the point where the Zambezi reaches its maximum power...
..the entire river flows over a cliff.
Over a mile wide...
..falling for over a hundred metres...
..500 million litres of water per minute.
So much water, it creates a plume of spray
that rises 500 metres into the sky...
..giving it the name of Mosi-oa-Tunya,
The Smoke That Thunders.
This is Victoria Falls.
The largest curtain of water...
..on Earth.
You would think it's a place to steer well clear of.
But there is temptation here.
A group of male elephants have come down to the edge of the river.
At this time of year, the islands right above the falls are lush
with tasty vegetation,
an elephant's paradise.
But to reach them is dangerous.
The Zambezi in full flood is a formidable force.
This is not the place to get swept away by the current.
But the lure of the islands is strong.
These males are prepared to take the risk.
The further they go,
the stronger the current gets.
And now it's getting deeper.
They are forced to swim.
Immediately, the current starts to drag them downstream.
They need to reach an island
or they could get swept over the falls.
One by one, they find their footing.
ELEPHANT TRUMPETS
But for smaller elephants,
the danger is greater.
At last, they are all safely across.
And right away, they start feasting on their prize
of rich vegetation.
But elephants can eat 300 kilos of food in a day.
So they'll soon get through all the tastiest pickings here...
..and will have to take their chances with Zambezi all over again.
Victoria Falls marks the next great transformation
for the Zambezi...
..as the entire river is swallowed up by a great chasm in the Earth.
Trapped in a channel just 25 metres wide,
the Zambezi now carves down through the rocky heart of Africa...
..forming sheer walls of 140 metres high.
This is the Batoka Gorge.
And it's here that the Zambezi conjures up another phenomenon...
..less well-known than Victoria Falls,
but just as unique.
The Zambezi Wave.
Surf perfection for those brave enough to try it.
It's crazy that you can bring something like surfing here.
Mikey February is a professional surfer.
He's here, 600 miles from the nearest ocean,
to surf the Zambezi Wave.
It's once in a lifetime, and only a few people have actually done it,
and I think that's, you know, one of the most special parts
of actually coming here.
Mikey has come to the Zambezi at a key point in the year.
As the dry season returns, over a period of three or four
months, the river changes again.
Victoria Falls starts to switch off.
Every year, the Zambezi goes through these dramatic cycles...
..with 50 times less water flowing over the falls when it's dry.
But it's as the water levels in the gorge start dropping
that conditions become just right for surfing.
When the water gets low enough,
it starts to interact with a rocky
shelf on the riverbed...
..and forms the Zambezi Wave.
A wave that stays in exactly the same place,
and breaks continuously.
But only lasts for ten days.
Even for a pro like Mikey,
the Zambezi Wave is not
to be taken lightly.
You have rocks, you have, you know,
hectic rapids and the water's moving
in such a different way to the ocean.
The fear factor is quite high.
Because the wave is formed by a slab of rock just beneath the surface,
surfing it is dangerous.
And then there are the rapids.
Mikey needs to get out of the white water as fast as he can,
before he gets swept downstream.
He paddles for the pickup point on the riverbank.
But the current is too strong.
This is where his experience in the water comes in.
He keeps calm.
And the safety kayaker is immediately on hand to help
guide him out of trouble.
Mikey is keen to try again.
The Zambezi Wave is pretty much like catching an ocean wave
but in reverse, because the ocean is pushing you forward and the river
is obviously going the opposite way.
It's just a completely different experience.
Once you get it the first time,
then you actually kind of get a gauge
of what you should be doing.
And you kind of know exactly what to expect when you fall.
I did get scared surfing this wave.
It's like a balance of, like, surfing, survival mode,
surfing, survival mode kind of thing.
I think the more time you spend in the river and on the wave,
you learn new things about it.
The way it moves and noticing its, you know, little subtleties.
It's also so beautiful, you know,
obviously you get to surf this wave,
but you also get to appreciate the Zambezi and everything
that it has to offer.
From the gorge, the Zambezi journeys on.
Winding its way through the fractured land along the border
between Zambia and Zimbabwe.
But it's about to shapeshift once more.
This time, at the hands of an entirely different force.
Kariba Dam.
Built in the 1950s,
it completely blocks the Zambezi,
and forces it to flow through its turbines to make electricity.
It took just five years for the river, held back
behind the dam,
to rise 100 metres.
Swelling up to form the vast Lake Kariba.
25 miles wide.
140 miles long.
44 cubic miles of water.
So much water that it caused over 20 large earthquakes as it settled
down on the land beneath.
By volume, Lake Kariba is the largest manmade lake
on the planet.
But it has also become a haven for wildlife.
Along the lake's shoreline, rich grasslands have grown up.
And in the forests of drowned trees
formed by the rising waters
is a unique habitat.
Perfect for the Zambezi's most iconic bird.
The African fish eagle.
There are around 500 breeding pairs here.
Each pair mates for life...
..the contorted shapes of the trees providing a platform
for their nests...
..protected by the crocodile-infested waters below.
The trees also provide the perfect vantage point
to survey the lake for prey.
On two-metre wings, they hunt for fish in the shallows.
This place is so good for fish eagles,
it has become their stronghold...
..their haunting call, the sound of Lake Kariba.
The Zambezi is now at the halfway point on its journey
to the Indian Ocean.
As its waters break free of the great dam,
the river flows on.
And now it enters a lost world,
spreading out into a valley 50 miles wide...
..nurturing a vast wilderness...
..some of the richest wildlife habitat in Africa.
It has also become world famous as one of THE places to come
and watch wildlife.
This part of the Zambezi and its tributaries is dotted
with safari lodges...
..places where people come to meet the Zambezi's iconic animals.
But who's watching who?
This safari lodge has operated for many years,
and the wild animals are now used to people.
And there's one main attraction just beyond the lobby.
A wild mango tree.
Its fruit is ripe for just a short time,
right at the end of the dry season.
A mouth-watering treat when food is scarce.
But it's not just baboons that have a thing for mangoes.
There are larger guests about to check into this lodge.
Elephants have been coming to this mango tree
from the river nearby for generations,
following ancient pathways that existed long before
the lodge was built.
One family in particular has learned that the lodge and its inhabitants
poses no threat.
Why go around?
When you can walk right through reception.
These are completely wild elephants.
But over the years, they have developed an understanding
with the staff here.
A trust passed down through elephant generations.
We've definitely developed that relationship and we've seen
youngsters grow into almost adults now over the years.
So it's it's a beautiful relationship we have.
This young bull probably first followed its mother
through here as a calf.
Now he is so relaxed,
he even takes time to browse the gift shop.
And check in at reception.
But soon, the lure of the mangoes is too great.
Trees like this are vital for the wildlife here.
Their roots draw water from deep underground,
so they can fruit even in the dry season.
An important source of energy and vitamin C.
And while the elephants are feasting,
the guests get a wild encounter of a lifetime.
When the elephants have had enough,
they quietly leave.
The same way they came in.
Straight through reception.
Elephants are big eaters.
But they also drink over 200 litres of water a day.
And for that, like all animals here, they rely on the river.
But the Zambezi is not only a place to get a drink.
For carmine bee-aters,
the banks of the river provide the perfect place to make a home.
Their colonies can contain up to a thousand nests...
..each one dug into the sandy cliff face over a metre deep...
..where their eggs are protected from predators.
But outside the nest, the adults are vulnerable.
African fish eagles don't only live on Lake Kariba -
they can be found all along the Zambezi.
The skills that make them so good at catching fish
work just as well for birds.
Hippos spend the hot days wallowing in the Zambezi's cool waters.
Schools of females live together in a territory ruled
by a single male.
And for the most part they are peaceful creatures.
Until the male's authority is challenged by a rival.
Then hippos turn violent.
In the safety of the river,
hippos are all-powerful.
It's as the sun goes down that they start to lose their bravado.
Hippos eat grass.
About 40 kilos every night.
They can't get that by staying in the river.
They may be huge - over two tons, but out of water
they become cautious.
So what are they nervous about?
As the night progresses...
..they travel further into the shadows.
Up to five miles a night.
Not making a sound.
Soon, the hippos are peacefully grazing in moonlit meadows.
But they are being watched.
Lions.
A pride of lions patrol this stretch of the Zambezi.
They know that animals are moving to and from the river,
and the dark is their friend.
But would they be bold enough to bother a two-ton hippo?
It's when the hippos start heading back to the Zambezi
that they are most vulnerable.
Lions have formidable eyesight.
As the night gets darker,
they gain the advantage.
Now anything is fair game.
A female lion tries for an impala.
Alarmed by the chaos, hippos scramble for the safety
of the river.
But a young hippo is on its own.
That doesn't go unnoticed.
A male lion is on to it.
Just in time.
The hippo makes good its escape,
safe once more in the waters of the Zambezi.
As the Zambezi journeys on, it performs a last
great feat of transformation.
Flowing down on to the coastal plains of Mozambique...
..it spreads out into countless sinuous branches...
..forming a great triangle that reaches all the way
to the Indian Ocean.
The Zambezi Delta.
But this last chapter of the Zambezi's journey
is haunted by the past.
From 1977 to 1992,
this place was ravaged by civil war.
The human cost was immeasurable.
And it had a devastating effect on wildlife.
During that war, wildlife was killed for the meat,
but also be killed for the ivory, for example, elephants,
everything just declined drastically.
Dominique Goncalves is a Mozambican conservationist who's passionate
about forging a brighter future for the wildlife here.
She is part of a team tasked to go into the heart of the Zambezi Delta,
to find out what has happened to the wildlife
since the devastation of the war.
Dominique is an elephant specialist.
Her plan is to put satellite collars on key elephants
to understand their movements.
The first step in protecting all the wildlife of the delta.
If you protect the area that an elephant uses, you're also
protecting a huge area that many, many other species are using.
But first, she has to find them.
The Zambezi Delta is vast -
over four and a half thousand square miles.
Once, the Delta was world-famous for its extraordinary
wealth of wildlife.
Great herds of elephant, and the largest numbers
of buffalo in Africa.
Since the civil war, few studies have been conducted here.
So little is known about what is left, but after just half an hour's
flying, there's an encouraging sign.
Elephants.
You really have to assess which individual we can work with.
So you have to think about the age and if it's a female, is she very,
very pregnant or not? If she has a young calf or not.
So you don't want to put an extra stress on her.
The dart contains a fast-acting sedative.
And by the time the helicopter has landed,
the elephant is already asleep.
A quick check on its breathing,
and they get to work.
They must work fast.
Though the elephant is sleeping peacefully,
the quicker they are, the quicker it can return to the herd.
And while the vet is fitting the collar,
Dominique gathers as much information as she can.
This is a rare opportunity to study these delta elephants.
Blood samples...
Her feet is very small.
..foot size,
and getting a record of what it's been eating is a crucial
but less glamorous part of the job.
All completed in just 15 minutes.
SNORING
Snoring!
A final shot reverses the effects of the sedative.
They now have just a couple of minutes to get airborne.
To encounter elephants so early in the trip is a hopeful sign
that good numbers are surviving in the delta.
In the next few days, Dominique successfully collars six elephants
from different herds.
And straight away, the collars start to deliver results.
She can see exactly where each elephant and their herd travels.
What space they need for socializing, feeding
and avoiding people.
Travelling the delta with their satellite collars,
Dominique's elephants are providing crucial hard data,
and are starting to map out the space that she hopes will
one day protect all the wildlife of the delta.
Even in such a brief visit,
there are tantalizing glimpses
of the life the delta could hold.
A great herd,
many hundreds of buffalo -
an echo of the legendary herds that once roamed here.
And a vision of what this place could be.
Here, where the Zambezi River
finally comes to the end of its journey.
The Zambezi River is extremely important.
Not only in terms of biodiversity and nature,
but give us culture,
give us, you know, livelihoods,
give us many things.
Perhaps without it, it wouldn't be the same.
I think that's the thing that makes us all so proud to have the Zambezi,
one of the greatest, biggest rivers in Africa,
to just finish here, next to home.
From a trickle of water in a far corner of Zambia...
..this great river has overcome many obstacles on its
1,500-mile journey.
The heat of the African sun...
..the rugged geology at the heart of the continent...
..the demands of a modern world...
..but wherever it flows, it brings life and opportunity.
No more so than here at the end of its journey...
..as the waters of the Zambezi
are finally carried away
by the Indian Ocean.
One of the biggest challenges for the Earth's Great Rivers team
was to film professional surfer Mikey February riding
the Zambezi Wave.
Timing was key.
This unique wave only appears for a few days each year...
..when water levels rise and fall with the rains.
It's also incredibly remote,
and dangerous to reach -
down steep, jagged cliffs
and through some of the most ferocious rapids
on the planet.
It's been quite the logistic nightmare, maybe, to organise.
We've had to postpone the shoot a few times just because the river
water levels are dropping, but they're not
dropping quickly enough.
And there's such a small window to sort of aim for,
for a wave that's surfable for Mikey.
But the team decide tomorrow is their best bet to head off
in search of the wave.
And to get everyone there safely are
the Zambezi's most experienced river guides.
This one as well.
We've got four cameras, two drones, all the batteries, accessories,
all the cards.
There's a lot of expensive kit
that could end up at the bottom of the Zambezi.
It's an early start,
and the team head to the edge of the gorge.
We're going to go down to the gorge now.
Please don't fall, don't slip, we're going just on ladders, so...
Lead river guide Sean
briefs the team on the treacherous 100 metre-descent ahead.
It's an almost vertical drop down sheer rock,
and along rickety wooden ladders.
All good in the hood? Yeah.
Has anyone fallen? All the time.
All the time!
It begins.
Lewis is the first to follow the guides down.
So far, so good.
Actually terrified.
But we must push forward.
The last thing the crew needs now is a twisted ankle or worse.
OK? I'm OK.
The team make it down to the Zambezi.
Actually never been more happy to get into a raft.
But the journey to find the wave has only just begun.
Precious cargo loaded.
Time to rock and roll. Let's go!
One, two, three!
At first, all seems calm, but turbulent water lies
just around the corner.
And the river starts to come alive.
The mighty Zambezi throws everything it can at them.
Whoa, whoa, whoa, whoa!
Suddenly, the raft hits a violent swell,
and sends camera operator Kevin hurtling into the rapids.
He must get out quickly before the river throws him
into the rocks or drags him under.
But he's in safe hands.
Thanks to the quick reactions of the guide, Kevin's pulled
back on board.
And the team finally make it
to the Zambezi Wave.
Months of meticulous planning went into arriving
at just the right moment.
But now it's all up to Mikey.
It's so scary, and it's so, you know, sort of dangerous.
When you see a photo of the river, when it's super low,
you can actually see the rock that it actually breaks
off of, and it kind of plays on your mind.
You know, you obviously have to wear a helmet,
and then you also have to wear a life jacket.
In the ocean, you're just wearing a wetsuit or board shorts
or something - you definitely feel out of your comfort zone.
But that's not Mikey's only concern.
Crocodiles, what's the situation?
So I mean, they're definitely here, and we can't discount them.
The danger zone is actually just this pool.
They don't like the fast-moving water.
So I think once you get
into the rapids, you're 100%, it's really just this area.
But I mean, we've all been watching, we've been looking, we've spoken
to the fishermen and they haven't seen crocs here for ages,
so I think we're good.
To get here at just the right time, Mikey and the team
have descended cliffs,
and navigated white water rapids.
But in return, they experienced an entirely new side of one
of Earth's great rivers.
Everyone's got a different relationship with this river,
and surfing that wave is mine.
Earth's great rivers...
..make extraordinary journeys...
..carving through continents,
feeding and connecting life...
..nurturing culture...
..providing a place for adventure.
From the frozen wilderness of the Yukon...
..to the tropical heat of the Zambezi...
HIPPO GROANS
..and the magical, hidden worlds of the Danube.
Great rivers are the lifeblood of planet Earth.
The majestic Danube...
..almost 2,000 miles long, from source to sea...
..running through the heart of Europe.
So much more than a single river.
The Danube is a giant network of water,
reaching out across the continent.
Flowing east from Germany and Austria,
all the way to Romania and the Black Sea.
Its tributaries gather water from 19 countries...
..making it the most international river on Earth.
On its journey, it will cross formidable landscapes
and ancient kingdoms...
..revealing glorious riches
and magical surprises.
But to follow the ever-changing face of this unique river...
..we start at the very top.
Over 4,000 metres above sea level,
Piz Bernina Mountain in Switzerland
is the highest point of the entire Danube system.
Here, 800 million tonnes of water
is locked in...as ice.
Four miles long and 250 metres deep,
the Morteratsch glacier, for most of the year,
is covered in deep snow.
But when temperatures rise in spring,
and conditions are just right...
..there's a window of opportunity.
Running keeps me alive.
It connects me with nature and connects me with my own spirit.
Anne-Marie Flammersfeld has spent most of her life running
the world's toughest landscapes.
Today, she is seizing her moment
to run on the frozen headwaters of the Danube.
Running on a frozen river, it's something really weird
because it's only there in a special period of time.
It looks beautiful,
but looks can be deceiving.
Even in the summertime, running on a glacier is really dangerous.
You don't know where the crevasses are.
When you fall into a crevasse, you can fall for three or five metres.
So it pays to follow a planned route.
I always try to look for the best line when I run downhill
because I run downhill really fast,
and I really enjoy it, and then my eyes are concentrated
on every step and, tak, tak, tak.
And, uh, yeah, this is most of the fun.
As she nears the base of the glacier...
..there's a glimpse of the true power locked up in the ice.
When you look into it and you see that the water
is coming from somewhere
and you think, "Ah, it's a river."
Beneath the glacier,
the headwaters of the Danube are on the move.
More than a quarter of the river's water
comes from the Alps.
And, in spring, it becomes an unstoppable force of nature...
..fuelling the flow of the Danube across the continent,
all the way to the Black Sea.
Its journey has only just begun.
A few miles away,
on the slopes of the valley below...
..the melting snow...
..makes way for new beginnings...
..revealing...
..someone's home.
Inside is a creature who has been waiting to come out...
..for nearly eight months.
A male alpine marmot.
They may seem small,
but, growing up to 8kg,
these are the heavyweights of the squirrel family.
Winter has not been easy on him and his kind.
Alpine marmots lose about a third of their body weight,
stuck in their burrows during winter.
Now, he needs to fatten up.
The melting snow has uncovered valuable food.
Marmots eat grasses, flowers,
and even a worm or two...
..if they can find them.
But there's a problem -
other families live here, too.
With only so much food to go around,
he'll need to defend his territory.
And when it comes to protecting home,
marmots mean business.
An intruder approaches.
It's time to go on the offensive.
To get an advantage...
..marmots rise up and stand tall.
Here in the valley, it's hand-to-hand combat...
..each pushing and grappling.
Now, keeping your footing is everything.
But just when the coast seems clear,
there's more danger.
The heat from the sun now causes giant icicles
to fall from frozen waterfalls.
A blow from one of these would spell disaster.
Crisis over.
In the valley of the marmots,
life is looking good.
As the meltwaters run on...
..they join countless other streams and tributaries...
..flowing from all corners of the Danube system.
Passing through a myriad of habitats,
some of which hide secret wonders.
In the forests of Bosnia,
one Danube tributary has a very different source.
These crystal clear waters are fed by underground springs...
..creating a magical water world.
Legend has it that the Romans were so stunned by this river's beauty
they named it Una, meaning "The one."
While the water may look clear,
it's full of dissolved minerals from the limestone below,
producing a special kind of river
with miniature waterfalls and pools.
As water flows over moss and other plants,
the dissolved minerals are gradually absorbed
and collected by this natural sponge,
which hardens and builds...
..eventually forming whole new waterfalls.
It's like something from a fairy tale.
But not everything to see here is above the water.
Below, there's a party under way.
The nutrient and oxygen-rich headwaters of the Danube
create the perfect place to gather and search for food.
Golden shoals of barbel
mix with graceful grayling, and busy trout.
Many use these fresh waters to spawn...
..including one species
found nowhere else on Earth.
Each spring, if you look carefully,
you'll find one of the river's top predators.
The huchen, also known as the Danube salmon,
can grow over a metre long.
The largest freshwater salmon in the world.
Today, this pair are showing their softer side.
With her powerful tail,
the female sweeps away the gravel
to make a small depression in the riverbed.
A nest in which to lay her eggs.
Very soon, the riverbed looks like it's had a spring clean.
The male joins her to mate...
..and guards her from any unwanted attention.
But then...
..perhaps it's best to leave these giant predators to it.
The secret waters of the Danube provide a bounty
of opportunity for life.
And where there are fish...
..others will surely follow.
Today, Zdena Gavranovic is hoping to catch a fish
that thrives in crystal clear waters,
the trout.
She starts by making some fishing flies.
IN CROATIAN:
IN ENGLISH: Her aim is to make the perfect insect...
..something that might just trick a trout to eat it.
IN CROATIAN:
Tiny feathers for the wings and silk for the body.
Solid enough to look the part,
yet delicate enough to cast.
Now, time to put them to use.
First, she casts out her line...
..with a loop in the air.
Released on to the water as light as she can...
..placing the fly to entice her quarry.
Fly fishing is a special kind of fishing.
IN CROATIAN:
Timing and rhythm are everything.
Each cast lets out a little more line...
..a little more hope.
IN CROATIAN:
No luck this time, not that it matters.
When a river is as beautiful as this,
that is rewarding enough.
While some are drawn to the tranquillity of the river,
the waters of the Danube constantly change.
In Slovenia, one of the Danube's largest tributaries,
the Sava, offers an entirely different experience.
Woohoo-hoo!
Like the rushing waters around him,
kayaker Rok Rozman finds a freedom here.
But it's not without risk.
There might be trees in the rapids,
which can be really dangerous.
There's some rocks that produce siphons.
So, like old people said,
the river is full of traps.
But, at the same time, the river is full of joy.
People who meet the river in a kayak
will always see the river differently.
For Rok, who is also a biologist,
rivers bring so much more than just enjoyment.
Cos the river has the most abundance in diversity
and life out of any habitat, you know?
Transporting nutrients, water, energy,
it's the most important part of nature.
And when faced with the pressures of life,
Rok also believes the river can help.
If you have problems,
you can go and talk to the psychiatrist,
or you can go and sit next to the river.
It's up to you what's nicer, cheaper, and better.
As they flow down from headwaters and alpine valleys,
the Danube tributaries finally come together
to become this great river.
Towns...
..farmland...
..and cities begin to line its route.
Over thousands of years, people have settled on its banks
and have tamed the river...
..straightened and engineered
to help protect against annual flooding.
But there are still wild places here.
Just outside Austria's capital, Vienna,
lies Danube-Auen National Park.
A strip of protected forest and wetland
on the banks of the Danube...
..home to some extraordinary creatures.
EARTH CRACKLES
A baby European pond turtle.
Buried as an egg four months ago,
it's now hatched and free.
Its mother chose a nesting spot that would be safe from flooding...
..but now it's far away from water.
And this tiny creature needs to go on an epic journey...
..all on its own.
But when you're the size of a thumbnail,
everything is so much larger.
Even tiny ants are a big deal.
But this turtle comes with its very own suit of armour.
Its arms and legs might be small,
but they are powerful.
Using all its energy,
it instinctively heads towards water.
Out of all the baby turtles that hatch every year,
only 2% will make it to adulthood.
And just when you think you've made it...
..the finish line seems so very far away.
And it's not just the turtles on the move.
BELL RINGS
Now or never.
A close shave.
Fortune favours the brave.
Critically endangered in Austria,
every turtle that makes it counts.
At last,
cool and refreshing water.
It might seem unfamiliar to our young turtle,
but, finally, home.
Safety, food, and even some friends.
Having passed through Germany, Austria and Slovakia,
the Danube is now at the midpoint on its great journey
and arrives in Hungary...
..at the majestic capital of Budapest.
A city that owes its existence to the Danube
and has seen empires rise and fall,
from the Romans to the Crusaders.
In Budapest, art and romance intertwine.
Grand architecture,
and no less than seven bridges,
showcase a place that has been the source
of cultural inspiration down the ages.
Today, with a population of 1.7 million,
it is as important as ever.
Water might be one of the oldest means of transport,
but it's still the cheapest.
And Budapest, because of its unique location,
is key to the Danube's continued success
as the backbone of the European transport network.
Up to 50 million tonnes of freight are transported
along the Danube each year.
Giant cargo ships and barges sail from port to port...
..carrying large and heavy loads,
like cereals, sand, and fuel
that would otherwise have to take less economical routes.
Dockyards act as transport hubs,
where shipping containers and goods are ferried like clockwork.
A giant, moving jigsaw puzzle,
working 24 hours a day,
seven days a week.
It's easy to see the importance of the Danube
to everyday life in Budapest,
but there is more.
A secret, hidden from view.
A shaded pool is hard to spot.
But, for two scientists,
it's an ancient wonder that connects the Danube
to the last Ice Age.
To explore it...
..Dr Gergely Balazs
and Dr Denes Szieberth
need to put on specialised equipment
as they prepare to enter a cave
that is completely filled...
..with freshwater.
The Molnar Janos caves only started to be explored in the 1950s,
with the invention of suitable diving equipment.
We have this busy city on the top of it.
But the cave, it's an ancient thing.
Crystal clear water,
filtered through rock over millennia,
stretches for almost four miles right under Budapest.
And there's more to be discovered with each dive.
Some of the passages here are huge,
and the water is so clean that you don't even see
that you are in the water.
So you are just flying through these huge spaces.
The caves offer unique opportunities for the scientists.
You see things which no-one have seen.
You make measurements which no-one had the opportunity to make.
This is pure exploration.
Despite the challenges,
the scientists have already begun to unlock
the secrets of these waters...
..concluding that over a million litres of water a day
flows imperceptibly through the caves.
And, in Budapest, there can only be one destination.
There is an obvious connection.
The cave feeds a lake,
which, through a channel under the Locash bath,
the water of this lake is flowing directly into the Danube.
A hidden tributary...
..joining the Danube on its great journey downstream.
Here, in Hungary,
the Danube's waters may seem slow and sluggish...
..but they still have the ability
to conjure up moments of wildlife magic.
On one of its middle tributaries...
..there's an animal that produces
one of the most spectacular natural events on Earth.
IN HUNGARIAN:
IN ENGLISH: Freshwater scientist Dr Bela Kiss
is trying to find some of them.
Bela monitors the population of an insect
that hides underwater for up to three years.
But, to do that...
..he has to dive down over four metres to the riverbed.
IN HUNGARIAN:
IN ENGLISH: It might not look like much...
IN HUNGARIAN:
IN ENGLISH: But in a few months, these larvae will transform
themselves to become one of the largest mayflies in the world.
For just a few days in June...
..when the water temperature rises,
they begin to hatch.
First, the males take flight.
IN HUNGARIAN:
IN ENGLISH: For some...
..life is very short indeed.
Soon, more and more appear from the water.
There's no time to hang around.
They have only three hours to live
and just one purpose...
..to find a female and mate.
The search for newly-hatched females
begins a frenzied mating dance.
The sky soon becomes thick, with several million mayflies
all mating in groups.
Once common in many parts of the Danube system,
pollution and habitat-loss
mean this great event is becoming harder to find.
But if you know where to look...
..it's an astonishing super-swarm of life.
IN HUNGARIAN:
As quickly as it began,
this remarkable event...
..is over.
After a three-year wait,
it's a short existence,
but it's a life well-lived.
In just one day, they have flown,
mated and died.
By this stage on its journey,
the Danube has been joined by its major tributaries,
the Drava, the Tisza...
..and the Sava.
Combined, they almost triple its flow.
As it reaches its third and final capital city,
Belgrade, in Serbia.
Over half a mile wide,
discharging 5.5 million litres per second.
This now mighty river...
..flows on towards the border with Romania
and one of the last great landmarks on its epic journey.
The Iron Gate gorge.
90 miles long, yet narrowing to just 150 metres wide.
For thousands of years,
all traffic on the river had to pass this daunting gateway.
The narrow gorge, with towering cliffs,
was infamous for its dangerous rapids and whirlpools...
..making passage in a boat extremely treacherous.
But in the 1970s,
this part of the Danube was changed forever...
..when engineers harnessed the river's power
and created the Iron Gates Dam...
..one of the largest hydroelectric plants in Europe.
This giant feat of engineering
produces five and a half million megawatts of electricity,
relied upon by 25 million people in Romania and Serbia.
A super-structure that has had an impact on both people...
..and the river.
Below the dam,
the Danube enters the lowlands of Romania and Bulgaria.
In these waters, there is one group of animals
that has been deeply affected by the man-made barrier upstream.
A true monster of the deep...
..the sturgeon.
Some species of sturgeon, such as the Beluga,
live for over 100 years and grow up to six metres long,
the size of a shark.
But it's their eggs that have made them famous,
sold as luxury caviar,
and shipped around the world.
As one of the major rivers draining into the Black Sea,
the Danube is a vital spawning ground for sturgeon.
But overfishing, pollution and the construction of dams,
which have blocked them from their spawning grounds upstream,
mean this river giant has all but disappeared.
Now, sturgeon are thought to be more critically endangered
than any other group of species...
..on the planet.
For one person, their future is something worth fighting for.
It's my passion.
I want to do it all the time.
Borislava Margaritova,
a fish biologist working in Bulgaria,
is trying to conserve the health of the Danube and its fish,
especially four species of extremely rare sturgeon still found here.
The Danube is the last river
in Europe that they spawn naturally.
So we try to protect them because they're very rare now.
Today, she's going out with her team to survey the river.
We are on the river at five in the morning
and we work most of the time until the evening time,
ten in the evening.
It depends what we catch.
Using nets, they hope to find some fish for their research.
But in such a large river,
and with a small team,
it's not going to be easy.
In nine years of doing this work,
Borislava and her team have only ever caught six sturgeon.
It's very difficult.
You spend eight, nine hours on the river, on the boat,
and you pick up the nets, and you see the empty nets.
It's very frustrating for me.
But there is always hope.
And today is a very special day indeed.
Yes!
HE SHOUTS
THEY CHEER
Incredibly, the team catch not just one sturgeon, but two.
Smaller than the famous Beluga, but no less precious.
A young sterlet sturgeon,
estimated to be between three and five years old.
And a starry sturgeon,
between five and seven years old.
Woo!
It's a huge result for the team.
We try to catch these specimens for months,
so it's very rare.
We are lucky. Ah-ha!
It's like when somebody have a birthday
and you have this present that you want for many,
many years...
HE CHEERS
..and you have it, and it's not only one, you have both.
They use their precious time with the fish
to record important data,
including size and weight.
And carefully attach tags,
so they can monitor the fish's movements.
The significance of this unique encounter is not lost on Borislava.
The sturgeons are like a flagship on the Danube.
So, if the sturgeon are still here,
we will know that the river is healthy.
There is a way to go.
But, for now, Borislava can celebrate this small victory.
Bye, baby.
It's hoped that conservation efforts,
like restocking and protecting migration routes,
might just give these iconic fish a future.
The Danube has finally arrived
at the last stage of its epic journey,
saving the greatest transformation till last.
The Danube Delta.
Passing through Romania and Ukraine,
this mighty river finally breaks free.
At almost 2,000 square miles,
this is the largest undisturbed wetland in Europe.
Only fully accessible by boat.
Narrow channels pass through riverine forests
of willow and poplar.
Opening out into freshwater marshes...
..fringed with reedbeds...
..and vast lakes covered in water lilies.
One of Europe's least inhabited places...
..giving space for wildlife to thrive.
More than 5,000 animal and plant species are found here.
The Delta is a globally important destination for birds,
some migrating from as far away as Africa and Asia to breed,
like Whiskered Terns and Squacco Herons.
And one bird that has made the Danube Delta its own.
The Great White Pelican.
With 17,000 breeding pairs...
..this is the largest colony in the world
outside of Africa and their numbers are increasing.
For just a few months,
they'll nest here and feed on the Delta's bounty...
..working together in giant flotillas to feast on fish.
A glorious spectacle at the end of the Danube's great journey,
before, once more, they head into the Black Sea and beyond.
The Danube's waters have flowed through more countries
than any river on Earth...
..through a continent separated by borders
and changed by humanity.
Despite these challenges,
always finding a way to keep going...
..to inspire...
..to nourish...
..and even astonish.
One continent connected and united...
..by water.
The Danube and its tributaries cover 19 countries,
creating the most international river system on Earth.
To capture its secret hidden worlds,
Earth's Great Rivers teamed up with local crews,
contributors and experts right across Europe...
..the people who know the Danube best.
But it was in Slovenia
that they met one person who revealed
a different side to the Danube story...
..a threat that could affect its future,
as well as many other rivers around the world.
Biologist and former Olympic rower -
Rok Rozman.
It's this mighty river that I call home.
The meaning of it is just extremely big in every way.
Rok has lived all his life on the Sava river,
one of the Danube's major tributaries...
..and he knows it as well as anyone.
Sava is really special
because it brings everything that's stored high up in
the mountains down to the bottom of the valley.
Without Sava, this valley wouldn't be green
and we wouldn't have pastures,
and we wouldn't have tourism.
We wouldn't be kayaking,
we wouldn't be fishing,
we wouldn't be enjoying the sound of the river.
It's basically the essence of this place.
Woohoo-hoo!
But it isn't just Rok who takes advantage of the power of rivers.
Over the years,
engineers have harnessed them across Europe
as a source of energy...
..building dams -
a valuable and low carbon source of electricity...
..and a way to store water and help control flooding.
But dams will always create winners and losers.
And these barriers have complex implications...
..dramatically reshaping the river's ecology
up and downstream...
WHISTLE TOOTS
..which is a concern
for many who live alongside these rivers.
The Sava river already has over ten dams
and there are plans for ten more.
For Rok,
the damage caused by these barriers to the wildlife
and ecology of the river is too great to ignore.
It would be sad to see
such destruction to this river, you know?
The river provides home for these animals.
You know, they can't go anywhere else.
If a bird lives on a gravel bar, well,
then it lives on a gravel bar.
If an otter needs a river with fish, well,
then that's what this river provides,
and that's why it's so important to protect these rivers.
And by the time we realise
the negative effects, it's already way too late.
And it just...
..breaks my heart and mind. Erm...
Because if these plans go ahead,
the place where I'm sitting right now will be underwater.
And it's not just me, I'm the last in line, you know?
My enjoyment in kayaking is the last in line.
There's fields here, people depend on these fields.
There's an otter family living there.
Where will the birds go? Where will the plants go?
Recent research has suggested more than a million barriers
fragment the continent's rivers.
The Danube and its tributaries
have seen more than 700 dams
and weirs built along their course.
The effect of these man-made structures
on wildlife is significant.
Faced with this, Rok decided to do something.
I realised that emotion without action
is basically going to ruin your soul eventually,
and I called a bunch of my friends and I said,
"Look, guys, these rivers are going to be destroyed without
"anybody knowing if we don't do something."
CHEERING
We realised that the core of the problem is that
there's not enough people spending time next to the river
and we said, "Well, we're going to take people rafting.
"We're going to take people picnicking by the river.
"We're going to take them kayaking, swimming, whatever."
You first need to know a place
to fall in love a place
and only then you're going to feel the need to protect it.
Rok's initiative has already helped stop
the building of 12 new dams in the region.
And one of the dams on his home river,
the Sava, has now been delayed.
But it's also focused attention on
the importance of allowing rivers to flow naturally.
Along with lakes and wetlands,
rivers cover less than 1% of the planet...
..and yet are home to a quarter of all vertebrate species...
..including over half of all species of fish.
Hydro is seen as a renewable source.
Their intentions might be good,
but the reality is that what we're doing is, basically,
we're destroying the most important parts of our environment.
Hydropower is a major low-carbon source of electricity,
but as decision makers are coming to understand
the value of free-flowing rivers...
..its use is being reassessed.
And a revolution in renewable technologies
may offer exciting alternatives...
..like solar...
..wind, and battery storage,
which could all help keep rivers flowing.
My hope for the future is that people realise
the importance of rivers for themselves...
..then also for all the wildlife and plants,
and whatever lives next to it...
..because the time is running out.
Earth's great rivers...
..make extraordinary journeys.
Carving through continents.
Feeding and connecting life.
Nurturing culture.
Providing a place for adventure.
From the frozen wilderness of the Yukon...
..to the tropical heat of the Zambezi...
..and the magical, hidden worlds of the Danube.
Great rivers are the lifeblood of planet Earth.
At the top of North America is a legendary river...
..flowing through some of the wildest country on Earth.
Relentless.
Immense.
For the First Nation people, it's seen as the Great River.
The Giver Of Life.
Its natural riches have long sustained all those
that live along its banks.
It gathers its waters...
..from vast ice fields...
..and great lakes...
..from mountain streams...
..and tundra plains...
..and brings life wherever it touches.
It seems all-powerful, but another force is at work here.
The cold of the Arctic winter.
When it strikes, this river is transformed.
It becomes a river of ice.
A frozen highway, upon which many will depend,
during the long, dark winter.
From icebound lifeline...
..to free-flowing giant.
This is the Yukon.
North America's great frozen river.
For 2,000 miles, the Yukon flows in a great arc
through northwest Canada and central Alaska to the Pacific Ocean.
Along the way,
it gathers water from an area four times larger than Great Britain.
But its story begins deep in the coastal mountain ranges
of British Columbia.
The Juneau Icefield,
1,500 square miles and nearly a mile deep.
The flood of summer meltwater from these glaciers
fuels the Yukon on its journey to the sea.
But this far north, the seasons change quickly.
As autumn temperatures plummet below zero,
the Yukon's tap turns off.
Soon, the entire river is hidden beneath a shield of ice.
Despite the October chill,
one of the Yukon's remote tributaries remains ice-free.
In Fishing Branch River,
thermal springs percolate from deep underground,
warming the stream just enough to keep it flowing.
It creates an opportunity for some of the Yukon's toughest characters.
For weeks,
chum salmon have been battling their way upstream from the Pacific.
Racing the freeze, they have swum over 1,500 miles,
following a long-remembered scent to reach their spawning beds.
On arrival, the females excavate shallow scrapes,
or redds, in the gravel.
Around them, the hook-jawed males tussle for prime position.
They need to be close to fertilise the thousands of eggs
the females release into their nests.
But spending so much time in the shallows leaves them vulnerable.
Up to 40 grizzly bears visit the creek
during the brief spawning season.
With air temperatures at 30 below,
wet fur quickly freezes, coating the bears in frost.
These are the Yukon's ice bears.
Unique, because the late salmon run means they can still hunt
when other grizzlies are already hibernating.
These cubs may lack the pioneering spirit.
Their mother certainly does not.
She keeps the first catch of the day for herself.
Her cubs are hungry
and determined not to miss out on breakfast.
They just need to find a way across the river.
Too slow.
Mum's straight back in the stream...
..chasing a second breakfast.
When her direct attack doesn't work, she gently paws the water,
encouraging the salmon into the shallows
where they can be picked off.
If the fishing is good, she will eat 30 kilos every day...
..feasting on the juiciest, energy-rich parts,
like eggs and skin.
But as the salmon run dwindles,
even old fish heads start to look appetising.
The bears need to put on enough weight
to see them through the long winter.
After a hard day's fishing, a good scratch helps them defrost.
Once the fish are gone,
even these tough ice bears will retire to their dens
to bed down for hibernation.
As the northern hemisphere faces away from the sun,
an intense cold now settles along the Yukon.
Across northern Canada and Alaska,
the Yukon is locked away beneath several metres of ice.
It will stay frozen for six months or more.
Temperatures tumble to -50.
As winter blizzards sweep along the Yukon Valley...
..the hard river ice is blanketed by snow.
In a land with few roads,
the frozen river becomes a highway through the forest.
And the skills needed to run these ice roads
still flourish along the Yukon.
I've been travelling on the river my whole life.
Kyla Boivin is a dog-sled racer
and the frozen Yukon is her racetrack.
I like how it all changes from mile to mile.
The land is so big.
It's the highway of the north, right?
She's putting her top team through their paces
along a section of the Yukon Quest challenge...
..a sled race billed the toughest on Earth.
It's a 1,000 mile test of endurance and teamwork,
run between Whitehorse in Canada and Fairbanks in Alaska.
Kyla has tackled this marathon seven times...
..the first when she was 18-years-old.
But now she rides just for the thrill of it.
The race harks back to a time when the frozen Yukon
was the only link between isolated settlements and the outside world.
Temperatures can be 50 below.
You can have a blizzard where it drops eight inches of snow
and the trail is gone.
There are spots that are just windswept
and it's barren and it's like the moon down there.
Kyla is following the same call of the wild
that drew the early pioneers to the Yukon.
You're only going to have six hours of daylight in the winter, right?
In the deepest winter.
And when it's dark you only see your head lamp beam.
That's not very far to spot trouble.
You are completely relying on the dogs
and they are completely relying on you.
And they're such wonderful creatures.
They're my favourite creatures on this planet, the sled dogs.
Definitely.
Even today, life for a musher and dog team out on the ice
is much the same as in those pioneering days.
Some straw for the dogs and a fire to melt snow for coffee
can make life a little more comfortable.
It's bitter, 25 below.
Ooph.
They're good dogs.
Once they see the straw, usually, these guys have camped a lot,
so they know straw means we're staying awhile.
Despite the cold,
the frozen river is a lifeline through these northern forests.
Even in deep midwinter, lynx are on the prowl.
Using the windswept ice river
means they can avoid deep, energy-sapping drifts.
Their huge furry paws act as snowshoes...
..helping them move effortlessly across soft snow.
Lynx are top predators...
..but a half-ton moose is way out of their league.
They have something much smaller in their sights.
Snowshoe hares can make up to 90% of their winter diet.
But being a specialist hunter brings its own problems.
Hare numbers rise and fall dramatically
in regular 10-year cycles.
In years with few hares, many lynx starve.
Even in good years,
pursuing such elusive prey means covering many miles a day.
As they wander these well-travelled highways,
lynx mark out their territories...
..with a squirt here...
..and a squirt there...
..leaving scent to help stake their claim to a stretch of frozen river
and to advertise for a mate.
These chemical signposts are the only way these loners
can keep in touch in such remote country.
And this really is North America's wild frontier.
Along the Yukon, there are no big cities and few roads.
Only four bridges span its 2,000-mile course.
Just 125,000 people live in the entire Yukon Basin.
Close to the Alaska-Canada border, 400 miles east of Anchorage,
is one of the few riverside towns - Dawson City...
..where the Yukon is joined by its most famous tributary...
..the Klondike River.
Dawson sprang up almost overnight
after gold was discovered here in 1896.
By the following year,
gold fever had lured 30,000 fortune hunters
to this remote river bank.
A lucky few struck it rich.
Most left empty-handed,
defeated by the Yukon's crushing hardships.
In just a few years, the gold petered out
and the rush was over almost as quickly as it started.
But Dawson lived on,
a beacon of light in a sea of wilderness.
One of the strangest reminders of those wild times
can be found in the Downtown Hotel saloon,
where the preserved frostbitten toe of a Yukon prospector
has become the key ingredient in a unique cocktail.
Taking the Sourtoe challenge has become a rite of passage
for anyone who visits Dawson today.
And if you dare, we can serve the toe.
Are you ready? I guess so.
You'd better be, cos here we go.
You can drink it fast, you can drink it slow,
but your lips must touch this gnarly toe.
Just your lips.
No teeth, no tongue, no tonsils.
Slainte.
Should I just do it? Oh.
You got it.
That was well done.
Perfect.
THEY LAUGH
Just when it seems the cold
will never release its grip on the Yukon...
..there's a sign in the heavens that change is coming.
The Aurora Borealis.
The Northern Lights.
These atmospheric light shows often reach their peak
just as the Earth's orbit
swings the northern hemisphere back towards the sun.
It marks a moment of transformation,
as new energy pulses along the Yukon.
Rising temperatures and the stirrings of long-dormant currents
open the first breaches in the frozen river's defences...
..just in time to greet thousands of noisy migrants to the Yukon.
Trumpeter swans have flown over 1,000 miles from southern Canada,
en route to their breeding grounds further north.
Marsh Lake gives these huge birds a chance to rest and refuel,
but only if their timing is spot on.
If they arrive before the thaw,
ice stops them feeding on the sedges that grow on the lakebed.
Arrive too late,
and spring floods put these plants beyond reach.
They've got it just about right,
although the cold April nights still glaze over the open water,
so the early risers must help break the ice.
Even for these long-necked birds,
it's a stretch to gather the vegetation a metre down.
Unable to reach the plants for themselves,
smaller migrants like wigeon stick close to the swans,
scooping up any leftovers.
After a short stay, it's time to move on,
chasing the spring thaw as it moves north.
The Yukon gathers its waters from across a vast backcountry...
..and it may take many more weeks
before the thaw reaches its Arctic tributaries.
Even in May, these are still frozen solid.
Rivers like the Porcupine.
500 miles long, its course takes it north across the Arctic Circle,
then back south to join the Yukon.
At its most northern point
is the First Nation Vuntut Gwitchin village of Old Crow.
Here, life revolves around subsistence fishing and hunting.
Winter in Old Crow can be harsh, it can be cold.
Being above the Arctic Circle,
we experience earlier winters and later springs.
The Porcupine River is the last,
one of the last large rivers to break up
and that's where we're at right now.
Every day, Paul Josie climbs the bluffs above the village
to scan the frozen river, watching and waiting.
As I stand and witness the changes in front of me from the river
and you hear the geese in the sky,
and the water trickling down the mountain
and you can feel the warm air on your face,
it gives me a sense that spring will be upon us.
There's one sign above all that means spring is close.
The arrival of the Porcupine caribou herd.
Over 200,000 animals on the move.
A 1,500-mile migration,
the longest by any land mammal on the planet...
..taking them to their calving grounds on Alaska's Arctic coast.
Early arrivals at the still-frozen Porcupine River,
mainly pregnant cows, walk across the ice.
But temperatures are rising rapidly.
Melting ice eases away from the banks
and starts to break up.
As more caribou arrive...
..they face a dangerous, shifting patchwork of unstable ice
and open water.
There's no way through.
They are forced to wait as a growing mass of ice
surges downstream towards Old Crow.
Slabs of ice jam against one another, blocking the river.
Some caribou get caught out,
marooned as the ice breaks up around them.
The lucky ones are carried back to shore,
miles further downstream.
Ice continues to build around Old Crow
until the pressure can no longer be contained.
It takes just a few days for many miles of river-ice to stream past,
heading for the Yukon.
Ever since I was young, the break-up of the river
has always been an exciting time for my community.
Watching the break-up is literally watching winter wash away.
The remaining caribou now take their chances with the ice.
Watching the Porcupine caribou swim across the river,
navigating through ice chunks...
..you get a sense of worry for this animal,
as you want them to succeed, you want them to cross
and you want them to be safe.
As the ice moves off downstream,
the stragglers make their way across the river...
..playing catch-up with the rest of the herd.
Winter is finally letting go.
Now that the river has broken up,
it's actually just waiting for more ice to clear,
waiting for it to be a little safer to travel.
And then I can put my boat in
and start travelling on our highway again.
After months of isolation,
the inhabitants of Old Crow can now reconnect with the Yukon.
As the great frozen river turns its back on the Arctic,
it starts to come alive.
Now bathed in near-continuous summer daylight,
temperatures continue to rise.
The snow and ice that brought the Yukon to a winter standstill
now re-energises the river.
With every stream and tributary adding its own pulse of meltwater,
the Yukon's power steadily grows.
With the flood comes something just as important as the water.
An ever-growing cargo of rock dust from distant glaciers...
..and mud from eroded valleys.
This meltwater flood
turns the Yukon into a formidable and relentless mud-filled giant.
Over the short summer,
the river will shift more than 80 million tonnes of sediment.
Most of it carried all the way to the ocean.
This unique mineral signature
now helps guide waves of salmon back to the Yukon.
Runs of chum, coho, pink and king salmon
battle their way hundreds of miles upstream
to spawn in the river's headwaters.
For thousands of years,
the indigenous First Nation peoples harvested the fish.
A summer bounty that fed them through the winter.
It's still a tradition for families
to head to remote riverside fish camps to catch and prepare salmon.
Sisters Faith Peters and Kathleen Peters-Zuray
from the Athabaskan First Nation
are heading to their camp at Rampart Rapids.
I'm middle of the river clan
and we've been surviving on king salmon all our life.
We've been coming to fish camp here for, like, 35 years.
Over those years,
the sisters have witnessed dramatic changes along the river.
Recently, the Yukon's many salmon runs have gone into steep decline...
..victims of a shifting climate and over-fishing in the Pacific.
Strict limits are now placed on catches
and if numbers of returning salmon are very low,
no fishing is allowed.
The family wait for this summer's decision,
relayed via the local Mukluk radio station.
RADIO: The pre-season projection does not meet the threshold
of 300,000 fish needed to allow subsistence fishing.
Therefore, subsistence salmon fishing will be closed
to begin the fall season.
Subsistence fishermen should prepare for continued closures.
Despite this bad news, the sisters are determined
to keep up the traditional knife skills they learnt as children.
It's hard for us to not to come to fish camp and to cut fish,
cos this is what we've been doing all our life.
With no fresh fish to cut,
Kathleen retrieves what's left of last year's catch
from the camp freezer.
Ooh, there you go.
We're ready.
This is one of salmon that was in the freezer from last year,
so it's a little soft, but it's still beautiful.
It's not even a job for us to do this. It's a happy vacation.
The strips are hung in the breeze to dry.
It's amazing that we're using frozen fish...
..and it's turning out pretty good.
It's going to taste like gold.
After a day in the sun,
the oil-rich strips are moved into the smokehouse.
The smoke helps preserve the fish
by creating a coating that slows decomposition.
In past years,
this smokehouse would be full to the rafters with salmon.
These few strips are a sad reminder of how bad things have become.
So there was no summer chum, no king and no fall chum.
That is...
..unprecedented.
We've never seen that.
It makes me sad. It really makes me sad, cos...
..for us to have a dinner without king salmon,
it's almost like starving.
It hasn't really hit me, really,
but we're losing a part of our culture.
It's...
It's devastating.
The sisters can only hope
next summer brings more salmon back to the Yukon,
so they can fill the smokehouse once again.
By September, autumn is colouring the Yukon's banks.
Bull moose are putting the finishing touches to something remarkable.
Every year, they grow a new set of antlers.
In older bulls, these can be two metres across and weigh 25 kilos.
Bulls need top-quality grazing to grow these huge racks
and lots of it.
Over 15 kilos every day.
Up to half their summer diet consists of water plants,
rich in protein and vital bone-growing minerals.
At their peak, the antlers are growing at two centimetres a day,
making them the fastest-growing organ in the animal kingdom.
All this effort is for just one thing - to get noticed.
And this bull's eye-catching headgear has already done its job.
All he needs to do now is dig a pit and soak the soil with his scent,
releasing pheromones that add to his already impressive allure.
He's irresistible.
Now over half a mile wide and still 700 miles from the sea,
the mud-filled Yukon swings southwards...
..into some of the wildest country in Alaska.
With no roads or rail links,
the few isolated villages here rely on the Yukon
to stay connected to the wider world.
Bush pilots can make some deliveries...
..while anything bulky must be carried by barge.
This is the last run of the season.
We do about between 13, maybe even 14,000 miles,
river miles, transporting cargo for customers.
Captain Lester Hakey has worked the Yukon for 26 years
and knows this autumn voyage is risky.
Most of the challenges are the river depth.
That's the biggest challenge.
It's only September, but the headwater streams
that feed the Yukon are already starting to freeze,
slowing the flow of water into the main channel
and river levels are dropping.
You got big river, you got wide river.
But you still have channels
where the river will go from 35 feet to six, seven, eight feet, you know,
and then you can get yourself stuck down there.
The currents are incredibly powerful...
..making navigation tricky
through constantly shifting bars and mudbanks.
And the barge doesn't stop just because the sun goes down.
They are on a tight schedule.
Lester shares the piloting with Sean Wright.
It's six hours on, six off, around the clock, seven days a week.
There's really nothing that we won't move.
If it's got wheels or if it can be picked up by heavy machinery,
we will haul just about anything that you can bring us.
We've got excavators, loaders,
we've got 70-foot long conveyor-belts on trailers.
Yeah. Keep on rolling, Sean. Looking good.
And with no docks or piers in the village,
deliveries are unloaded down make-shift ramps.
We've got people's personal vehicles.
Thanks a lot. All right, dude.
All I do is get it from point A to point B, man.
Oh, yeah. Yeah. Here you go.
People's food, groceries, soda cans.
Building materials.
Yeah, just about anything you can think of.
If anything has been forgotten,
it's eight months before the spring thaw allows deliveries again.
The barge's most precious autumn cargo
is 700,000 litres of fuel.
It's what villagers rely on to warm their homes
and run their vehicles once winter comes.
I love the challenge.
I love the challenge of the whole thing. It's just...
It's awesome because when you get done, and you're, you know,
you think you've been beat,
and then all of a sudden you get it done, and everybody's happy
and you got the freight off to the people and they're happy...
..you feel a sense of accomplishment, you know? Yeah.
That's part of the reason why I love this, you know.
I mean, you can't beat this office to work in, can you?
I mean, really.
After the last delivery, it's an eight-day battle back upstream
to their winter quarters before the river freezes.
Meanwhile, the Yukon, now at its widest, and most remote,
forges westward into a very different world.
With the mountains far behind,
there's now almost no gradient left to drive the river forwards.
Across this flat, exposed landscape, the Yukon slows and spreads,
splitting into a tortuous network of meandering channels.
Breaking up this maze of waterways is an endless boggy tundra...
..pockmarked with thousands of ponds.
This is the Yukon Delta...
..covering over 50,000 square-miles, an area larger than England.
At the very end of its journey, the Yukon has one final surprise.
Rising out of the waters surrounding the southern delta is Nelson Island.
Here, at the very edge of the continent,
live some remarkable creatures.
Musk ox.
With their fine woolly coats, these relics of the last Ice Age
can shrug off the very worst delta weather.
Days are spent gathered in small family groups.
A tight-knit sisterhood of cows with their calves
and one very large bull.
He's trying his best to corral the wandering females...
..constantly checking if any are ready to mate.
It's the rutting season
and his harem has caught the eye of a young bull,
who fancies his chances.
As the herd drifts over the hills...
..the hopeful youngster follows, slowly getting closer.
Finally, his presence forces the resident bull to react.
This is all about intimidation...
..as rivals assess each other's size and strength.
A few tentative shoves
and this youngster quickly realises he's more than met his match.
During the rut,
contests like this are kicking off all over the tundra.
If rivals are evenly matched,
things can escalate into full-blooded confrontation.
Thick skulls and ten-centimetre horn bosses act like helmets
protecting them from these earth-shaking collisions.
Intruder seen off.
The victor has won the chance to father next year's calves.
But now, across this wilderness,
all musk ox turn to face the greatest challenge of the year.
After the freedom gained during the intense summer...
..the Yukon must once more yield to the power of an Arctic winter.
The first snows already blanket the high country.
Cold is silently creeping back along the valleys.
This year's salmon runs may have been poor...
..but some fish have made it back to their spawning streams.
As life along the Yukon turns full circle...
..this is where their journey will ultimately end.
Their deaths will help others to survive the winter.
And this is not the end of their story.
Nurtured by the Yukon's waters, salmon eggs pulse with life.
For the salmon...
..and all those living in this wild country,
the river holds the key to the future.
The Yukon will always be the natural and spiritual heart
of this great wilderness.
North America's legendary frozen river.
For the Earth's Great Rivers team,
the challenge of filming in the Yukon
was in finding ways to access one of the most remote regions on Earth.
A mission that took them on many intrepid adventures.
But it all started with an old school bus.
Once an ordinary school bus,
now it's on the ultimate field trip for the BBC.
So our small crew is completely self-sufficient
when we're out in this bus.
As well as making all the power from the solar,
we are kitted out with VHF radio, satellite phones.
We also have a cell booster,
which will help amplify any cell service that might be in the area.
I think if I just park in here.
Travelling with everything they need,
the crew head into the river's far-flung headwaters region.
They have set themselves the challenge of capturing
a series of dynamic shots of creeks throughout the year,
with the camera moving fast,
just a few centimetres above the water's surface.
Camera operator Ollie is adapting a First Person View Drone,
or FPV, for the task.
These are the FPV drones.
These allow us to see from the perspective of the drone
as we're flying, which allows us to get much tighter shots,
go through smaller gaps,
which we just wouldn't be able to do safely with these bigger drones.
Not only does the drone need to be waterproof,
but we need to be able to retrieve it and it not sink if it does crash,
so we've got these quite high-tech pool floats
with ping-pong balls in them.
So I'm just going to test them out.
Success. It floats.
Having survived the bathtub test, it's time to try it for real.
Let's give this a go.
Using a headset, Ollie can see from the perspective of the drone.
Well, they add quite a bit of weight.
It's a process of trial and error,
which the crew will perfect through their time filming.
And different creeks present different challenges,
both for flying and for retrieving the drone.
Fingers crossed. What could go wrong?
As winter draws in, the task becomes increasingly difficult
and drone recovery becomes even more nerve-racking.
Despite the mishaps, Ollie's drone has worked,
delivering a completely new perspective.
Dramatic low-level shots along some of the wildest
and most inaccessible parts of the Yukon.
To capture the final chapter of the Yukon's story,
the crew have to leave the bus behind
and embark on their most challenging journey of all.
To film musk ox herds that roam a remote island
where the Yukon empties into the Bering Sea.
Standing in their way is the Yukon's vast roadless delta.
The only way across is by plane.
Waiting for them in the remote village of Toksook Bay
is local Yupik guide Jackie Cleveland,
who has organised some unusual accommodation
in this rarely-visited community.
It's very remote here. There are no hotels.
So this is the Nelson Island School, where we will be sleeping.
Jackie introduces the class to the crew.
UNTRANSLATED
So here is the library,
which we've turned into a sleeping space slash office.
This is one bedroom. Cosy.
And then another bedroom is down here.
Neat.
With their base camp set up,
the team set off on the next leg of their wild journey...
..this time taking to all-terrain vehicles.
The best way to navigate the island is to follow the coastline.
The flat beaches make for faster going
than the dense tundra that cloaks the interior of the island.
But this route has its own challenges.
We're in a bit of a race against the tides.
We have an hour to get there and if we don't make it back,
we're stuck there.
So time's on. Pressure's on.
With the tide coming up, the crew's travel corridor is shrinking.
And they still haven't seen any musk ox.
With the way ahead disappearing fast,
they have no option but to head inland.
Up here, it can take an hour to cover just one mile.
After hours of bumpy travel,
the team reach areas where even the ATVs struggle.
The only option is to send a drone up
to help scope out the endless rolling hills.
They spot a herd, sheltering in one of the island's hidden valleys.
Thanks to the drone, the crew can at last start filming.
Spending time with these magnificent animals
makes a fitting end to a journey that has taken the crew
to the wildest parts of one of the wildest rivers on Earth.