Narrator: The majestic Danube.

Running through the heart of Europe.

So much more than a single river.

♪ The Danube is a giant network of water reaching 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 epic journey, it will cross formidable landscapes... and ancient kingdoms... revealing glorious riches... and magical surprises.

♪ 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 growling] and the magical, hidden worlds of the Danube.

Rivers are the lifeblood of planet Earth.

♪ Narrator: The story of the Danube is an extraordinary one.

To reveal the magical and surprising character of this unique river, we start... at the very top.

Over 13,000 feet above sea level, Piz Bernina mountain in Switzerland is the highest point of the entire Danube system.

Here, almost 900 million tons of water is locked in as ice.

The Morteratsch glacier, 4 miles long and 800 feet deep, is covered in snow for most of the year.

But when temperatures rise in spring, and conditions are just right... there's a window of opportunity.

Woman: Running keeps me alive.

It connects me with nature and connects me with my own spirit.

Narrator: 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.

Flammersfeld: Running on a frozen river, it's something really weird, because it's only there in a special period of time.

Narrator: It looks beautiful, but looks can be deceiving.

Flammersfeld: 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 3 or 5 meters.

Narrator: So, it pays to follow a planned route.

Flammersfeld: 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, er, yeah, this is most of the fun.

Narrator: As she nears the base of the glacier... there's a glimpse of the true power locked up in the ice.

Flammersfeld: When you look into it and you see that the water is coming from somewhere, and you think, "Ah, it's a river!"

Narrator: 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... fueling the flow of the Danube River 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 valleys 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 8 months.

A male alpine marmot.

They may seem small, but growing up to 16 pounds, these are the heavyweights of the squirrel family.

Winter has not been easy on him and his kind.

Alpine marmots lose about 1/3 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.

[Marmot calling] ♪ 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 its 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 starts to build... 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 underway.

These 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 3 feet long.

The largest freshwater salmon in the world.

Today, this pair are showing their softer side.

They're here to perform a mating ritual.

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 headwaters 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.

[Gavranovic speaking native language] Narrator: Her aim is to make the perfect insect.

Something that might just trick a trout to eat it.

[Gavranovic speaking native language] Narrator: 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 onto the water, as light as she can.

Placing the fly to entice her quarry.

Fly fishing is a special kind of fishing.

[Gavranovic speaking native language] Narrator: Timing and rhythm are everything.

Each cast lets out a little more line.

A little more hope.

♪ [Gavranovic speaking native language] Narrator: 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 tranquility of the river... others look for something entirely different.

In Slovenia, spring meltwater from the mountains has swollen one of the Danube's largest tributaries.

Which is irresistible for one local kayaker.

Rok Rozman has lived on the banks of the Sava River all his life.

Rozman: It's this mighty river that I call home.

The meaning of it is just extremely big in every way.

Narrator: It has a way to go before it reaches the main flow of the Danube, but for Rok... this early part of the river is full of possibilities.

Rozman: Whitewater kayaking is a, it's not really a sport, it's a way of life.

You base your life on what the river does.

But in general, the process is simple.

You go to the top of the river and you follow the flow downstream and try and have fun while doing it.

Narrator: Rok's idea of fun is more extreme than most.

And spring on the Sava is the ideal time to find it.

♪ Rozman: Woo hoo hoo.

Narrator: Like the rushing waters around him, he finds a freedom here.

But it's not without risk.

Rozman: 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.

Narrator: For Rok, who is also a biologist, rivers bring so much more than just enjoyment.

Rozman: 'Cause 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.

Narrator: And when faced with the pressures of life, Rok also believes the river can help.

Rozman: 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.

Narrator: As they flow down from headwaters and alpine valleys... the Danube tributaries finally come together... to become this great river.

[Distant bells tolling] 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 Donau Auen National Park.

A strip of protected forest and wetland on the banks of the Danube.

Home to some extraordinary creatures.

A baby European pond turtle.

Buried as an egg 4 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 armor.

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 each year, only 2% will make it to adulthood.

And just when you think you've made it... the path to success seems so very long.

And it's not just the turtles on the move.

[Bicycle bell ringing] Now or never.

♪ [Bell rings] ♪ A close shave.

Fortune favors the brave.

Critically endangered in Austria, every turtle that makes it counts.

♪ At last, cool and refreshing water.

It might at first seem unfamiliar for our young turtle, but finally, it's home.

Safety, food... and even some friends.

[Bird squawking] Having passed through Germany, Austria, and Slovakia, the Danube is now at the midpoint of 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 7 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 55 million tons 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, 7 days a week.

It's easy to see the importance of the Danube to everyday life in Budapest, but there's more.

♪ A secret, hidden out of 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.

[Door closes] To explore it... Dr. Gergely Balazs and Dr. Dénes Szieberth need to put on specialized 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.

Man: We have this busy city on the top of it.

But the cave, it's an ancient thing.

Narrator: Crystal-clear water... filtered through rock over millennia... stretches for almost 4 miles right under Budapest.

And there is more to be discovered with each dive.

Man: 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.

Narrator: The caves offer unique opportunities for the scientists.

Man: You see things which no one have seen.

You make measurements which no one had the opportunity to make.

This is pure exploration.

Narrator: Working here does not come without risk.

Man: I think what's special about cave diving is that if everything goes fine, you don't feel the danger.

Because you are just swimming around in a beautiful environment and you are weightless and, er, it's all quiet.

And you have to remind yourself that this is not your environment, you need all this equipment to survive there... and I think you have to remind yourself all the time that it doesn't matter how you feel now, it can change in a second.

Narrator: Despite the challenges, the scientists have already begun to unlock the secrets of these waters... concluding that over 200,000 gallons of water a day flows imperceptibly through these 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.

Narrator: 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.

[Man speaking native language] Narrator: 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 3 years... but to do that, he has to dive down over 10 feet to the riverbed.

[Kiss speaking native language] Narrator: It might not look like much... [Kiss speaking native language] Narrator: 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.

[Kiss speaking native language] Narrator: For some... life is very short indeed.

♪ Soon, more and more appear from the water... flying to the trees, where they will transform... into sexually mature adults.

There's no time to hang around.

They have only 3 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.

[Speaking native language] Narrator: As quickly as it began... this remarkable event... is over.

After a 3-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 of 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 1.5 million gallons 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 shrinking to just 500 feet 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 5 1/2 million megawatts of electricity, relied upon by 25 million people in Romania and Serbia.

A superstructure 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 manmade 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 over 20 feet 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, have hit the sturgeon hard.

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.

Narrator: Borislava Margaritova, a fish biologist working in Bulgaria is trying to conserve the health of the Danube and its fish... especially 4 species of extremely rare sturgeon still found here.

Margaritova: The Danube is the last river in the Europe that they spawn naturally, so we try to protect them because they're very rare now.

Narrator: Today, she's going out with her team to survey the river.

Margaritova: We are on the river at 5:00 in the morning, and we work most of the time until the evening time, 10:00 in the evening.

It depends what we catch.

Narrator: 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 9 years of doing this work, Borislava and her team have only ever caught 6 sturgeon.

Margaritova: It's very difficult.

You spend 8, 9 hours on the river, on the boat, and you pick up the nets and you see the--the empty nets.

It's very frustrating for me.

Narrator: But there is always hope.

And today is a very special day indeed.

Man: Yes!

[Speaking native language] [Laughs] Narrator: Incredibly, the team catch not just one sturgeon, but two.

[Man speaking native language] Narrator: Smaller than the famous beluga, but no less precious.

A sterlet sturgeon between 3 and 5 years old... and a young starry sturgeon, between 5 and 7 years old.

Man: Whoo!

Narrator: It's a huge result for the team.

Margaritova: We try to catch these specimens for months, so it's very rare.

It's--we are lucky guy.

Ha ha ha!

Margaritova: It's like when somebody have a birthday, and you have this present that you want for many, many years... [Shouting indistinctly] and you have it and it's not only one, you have both.

[Laughs] Narrator: They use their precious time with the fish to record important data... [Margaritova speaking native language] Narrator: 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.

Margaritova: The sturgeons are like a flagship on the Danube, so if the sturgeon are still here, we'll know that the river is healthy.

[Sprays] Narrator: There is a way to go.

Yes!

Very good.

But for now, Borislava can celebrate this small victory.

[Margaritova speaks native language] Narrator: 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 surprise 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.

A place that is only really accessible in one way.

Man: One of the main ways to be able to-- to see the natural beauties of the Danube Delta is to travel around in boats, er, that are very quiet.

Narrator: Sebastian Bugariu, a Romanian biologist... knows that you need to slow down... to discover the secrets of the Delta.

Bugariu: You can find very beautiful things in the Delta almost all the time.

Narrator: As the Danube opens out onto endless freshwater marshes... and vast lakes covered in water lilies... it is at its wildest.

One of Europe's least inhabited places.

Bugariu: Still a very wild place and due to the fact that it has been kept in a natural state for a very long period of time, it is the place where many bird populations have found a--a refuge.

Narrator: There are more than 300 species of birds here.

The delta is a globally important destination, 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, heading 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, but despite these challenges, always finding a way to keep going, to inspire, to nourish, and even astonish.

One continent, connected and united... by water.

"Rivers of Life", Season 2 is available on Amazon Prime Video ♪ ♪