Only 3% of the water on our planet is fresh.
Yet these precious waters are rich with surprise.
All life on land is ultimately dependent upon fresh water.
The mysterious tepuis of Venezuela.
Isolated mountain plateaus rising high above the jungle.
This was the inspiration for Arthur Conan Doyle's Lost World,
an imagined prehistoric land.
Here, strange towers of sandstone have been sculptured
over the millennia by battering wind and torrential rain.
Moisture, rising as water vapour from the surface of the sea, is blown inland by wind.
On reaching mountains, the moist air is forced upwards and, as it cools,
it condenses into cloud and finally rain, the source of all fresh water.
There is a tropical downpour here almost every day of the year.
Fresh water's journey starts here, high in the mountains.
Growing from humble streams to mighty rivers, it will travel hundreds of miles to the sea.
Angel Falls, the highest waterfall in the world.
Its waters drop unbroken for almost 1,000 metres.
Such is the height of these falls
that long before the water reaches the base in the Devil's Canyon,
it's blown away as a fine mist.
In their upper reaches, mountain streams are full of energy.
Streams join to form rivers, building in power, creating rapids.
The water here is cold, low in nutrients but high in oxygen.
The few creatures that live in the torrent have to hang on for dear life.
Invertebrates dominate these upper reaches.
The hellgrammite, it's body flattened to reduce drag,
has bushy gills to extract oxygen from the current.
Blackfly larvae anchor themselves with a ring of hooks.
But if these become unstuck, they are still held by a silken safety line.
There are advantages to life in the fast stream.
Bamboo shrimps can just sit and sift out passing particles with their fan-like forearms.
Usually these mountain streams only provide enough food for small animals to survive.
But with the spring melt here in Japan, monsters stir in their dens.
Giant salamanders, the world's largest amphibian, almost two metres long.
They're the only large predator in these icy waters.
They begin their hunt at night.
These salamanders have an exceptionally slow metabolism.
Living up to 80 years, they grow into giants.
The fish they hunt are scarce, and salamanders have poor eyesight.
But sensory nodes on their head and body detect the slightest changes in water pressure.
Free from competition, these giants can dine alone.
Pickings are usually thin for the salamanders.
But every year some of the world's high rivers are crowded by millions of visitors.
The salmon have arrived.
This is the world's largest fresh-water fish migration.
Across the northern hemisphere, salmon returning from the ocean to their spawning grounds
battle their way for hundreds of miles upstream.
Up here there are fewer predators to eat their eggs and fry.
A grizzly bear.
From famine to feast, he is spoilt for choice.
This Canadian bear is very special.
He has learnt to dive for his dinner.
But catching salmon in deep water is not that easy, and the cubs have lots to learn.
The annual arrival of spawning salmon
brings huge quantities of food into these high rivers that normally struggle to support much life.
Although relatively lifeless, the power of these upland rivers to shape the landscape
is greater than any other stage in a river's life.
Driven by gravity, they are the most erosive forces on the planet.
For the past five million years, Arizona's Colorado River has eaten away at the desert sandstone
to create a gigantic canyon.
It's over a mile deep and at its widest, it's 17 miles across.
The Grand Canyon.
This river has cut the world's longest canyon system.
A 1,000 mile scar, clearly visible from space.
As rivers leave the mountains behind, they gradually warm and begin to support more life.
Indian rivers are home to the world's most social otter.
Smooth-coated otters form family groups up to 17 strong.
Group rubbing not only refreshes their coats but strengthens social bonds.
When it comes to fishing, there is real strength in numbers.
Fishing practice begins when the cubs are four months old.
Only the adults have the speed and agility needed to make a catch.
Adults share their catches with their squabbling cubs.
Most otters are solitary,
but these rich warm waters can support large family groups,
and even bigger predators.
Mugger crocodiles, four metres long, could easily take a single otter.
But confident in their gangs,
the otters will actively harass these great reptiles.
Team play wins the day.
The Mara River, snaking across the plains of East Africa.
As the land flattens out, rivers slow down and lose their destructive power.
Now they're carrying heavy loads of sediment that stains their waters brown.
Lines of wildebeest are on the march.
Each year, nearly two million animals
migrate across the Serengeti plains in search of fresh green pastures.
For these thirsty herds, the rivers are not only a vitalsource of drinking water
but also dangerous obstacles.
This is one of the largest concentrations of Nile crocodiles in Africa,
giants that grow over five metres long.
From memory, the crocodiles know the wildebeest are coming, and gather in anticipation.
The crocodile's jaws snap tight, like a steel trap.
Once they have a hold they never let go.
It took over an hour to drown this full grown bull.
To surprise their prey, the crocodiles must strike with lightning speed.
Here, only the narrowest line
separates life from death.
Most rivers drain into the sea, but some end their journey in vast lakes.
Worldwide, lakes hold 20 times more fresh water than all the rivers.
The East African Rift Valley holds three of the world's largest,
Malawi, Tanganyika and Victoria.
Lake Malawi, the smallest of the three, is still bigger than Wales.
Its tropical waters teem with more fish species than any other lake.
There are 850 different cichlids alone,
all of which evolved from just one single ancestor
isolated here thousands of years ago.
These two-metre wide craters are fish-made.
Fastidiously maintained by the males, these bowers are courtship arenas.
Cichlids are caring parents.
Brooding young in their mouth is a very effective way of protecting them.
This lake can be a dangerous place.
After dark, predatory dolphin fish emerge from their daytime lairs among the rocks.
Like packs of sharks, they are on the prowl for sleeping cichlids.
In the darkness,
these electric fish hunt by detecting distortions in the electric field they create
around their bodies.
Any cichlid that ventures out will be snapped up.
The floor of Lake Malawi drops 700 metres into an abyss.
Here in this dead zone, the larvae of lake fly midges hide out away from predators.
In the rainy season, they balloon up to the surface and undergo a magical transformation.
At dawn, the first adult midges start to break out.
Soon, millions upon millions of newly hatched lake flies are taking to the wing.
Early explorers told tales of lakes that smoked, as if on fire.
But these spiralling columns, hundreds of metres high, are mating flies.
Once the flies have mated, they will all drop to the water surface, release their eggs and die.
Malawi may look like an inland sea,
but it is dwarfed by the world's largest lake,
Baikal in eastern Siberia.
400 miles long and over a mile deep,
Baikal contains one fifth of all the freshwater
found in our planet's lakes and rivers.
For five months of the year, it is sealed by an ice sheet over a metre thick.
Baikal is the oldest lake in the world
and despite the harsh conditions, life flourishes here in isolation.
80% of its species are found nowhere else on Earth,
including the world's only fresh water seal.
With this seal and its marine-like forests of sponges,
Baikal seems more like an ocean than a lake.
There are shrimp-like crustaceans, giant amphipods as large as mice.
They are the key scavengers in this lake.
The water here is just too cold for the bacteria that normally decompose the dead.
Most rivers do not end in lakes but continue their journey to the sea.
The planet's indisputable super-river is the Amazon.
It carries as much water as the next top-ten biggest rivers combined.
Rising in the Peruvian Andes, its main trunk flows eastwards across Brazil.
On its way, the system drains a third of South America.
Eventually over 4,000 miles from its source it empties into the Atlantic Ocean.
The Amazon transports a billion tons of sediment a year, sediment clearly visible
at the "mixing of the waters" - where one massive tributary, the Rio Negro, flows into the main river.
Its waters are wonderfully rich.
To date, over 3,000 species of their fish have been described,
more than in the whole of the Atlantic Ocean.
The Amazon is so large and rich in fish that it can support freshwater dolphins.
These botos are huge, two-and-a-half metres long.
In these murky waters, they rely on sonar to navigate and hunt.
They work together to drive shoals of fish into the shallows.
Botos are highly social, and in the breeding season there is stiff competition for mates.
The males hold court in an unique way.
They pick up rocks in their jaws and flaunt them to their attending females.
Maybe each male is trying to show how strong and dextrous he is
and that he therefore is the best father a female could have for her young.
Successful displays lead to mating.
Even for giant rivers like the Amazon
the journey to the sea is not always smooth or uninterrupted.
Iguassu Falls, on the border of Brazil and Argentina,
is one of the widest waterfalls in the world, one-and-a-half miles across.
In flood, 13 million litres of water spill over every second.
All the world's great broad waterfalls -
Victoria, Niagara and here Iguassu,
are only found in the lower courses of their rivers.
In their final stages, rivers broaden and flow wearily across their flat flood plains.
Each wet season here in Brazil,
the Parana river overflows its banks and floods an area the size of England.
The Pantanal, the world's largest wetland.
In these slow-flowing waters, aquatic plants flourish,
like the Victorian giant water lily, with leaves two metres across.
These underwater forests are nursery grounds for fish.
Over 300 species breed here, including red-bellied piranha.
And other predators, like the spectacled caiman.
Ripening fig trees, overhanging the water's edge,
provide welcome food for shoals of hungry fish.
The commotion attracts dorado, known locally as the river tiger.
They patrol the feeding shoals, looking for a chance to strike.
And waiting in the wings, ready to pick off any injured fish, are the piranhas.
A feeding frenzy quickly develops.
Piranha can strip a fish to the bone in minutes.
Great numbers of fish sustain vast flocks of water birds.
The roseate spoonbill is just one of the 650 bird species found in the Pantanal.
They nest alongside wood storks, in colonies thousands strong.
Spectacled caiman linger below, waiting for a meal to fall out of the sky.
When rivers finally reach the sea, they slow down, release their sediment and build deltas.
In Bangladesh, the Ganges and Brahmaputra rivers join to form the world's biggest.
Every year, almost 2,000 million tonnes of sediment,
eroded from the Himalayas is delivered to the ocean.
At the delta's mouth, the largest mangrove forest in the world, the Sunderbans.
These extraordinary forests spring up throughout the tropics
in these tidal zones where rivers meet the sea.
Crab-eating macaques are mangrove specialists.
In Indonesia,
these monkeys have adopted a unique amphibious lifestyle.
They fish out fallen food.
The troop also uses the waters to cool off during the heat of the day.
But the channels are also the playground for restless young macaques.
Some of the young have even taken to underwater swimming.
They can stay down for more than 30 seconds
and appear to do this just for fun.
Yet these swimming skills, acquired during play,
will certainly be useful later in life in these flooded mangrove forests.
In cooler climes, mud laid down in estuaries
is colonised by salt-marsh grasses
and form one of the most productive habitats on the planet.
400,000 greater snow geese flock to the estuaries along the Atlantic coast of the United States
to rest and refuel on their long migratory journeys.
This is the end of the rivers' journey.
Collectively they've worn down mountains and carried them to the sea.
And all along the way, their fresh water has brought life in abundance
to planet Earth.
Filming piranhas in a feeding frenzy in the wild
has rarely, if ever, been attempted
and it was to prove the freshwater team's greatest challenge.
Welcome to the piranhas' country.
Arriving in the Pantanal
with over a tonne of dive and camera equipment,
producer Mark Brownlow and his team were heading into uncharted waters which had never been dived before.
The piranha lives everywhere. It is the most common fish here.
I have a gift for Peter. This will give a good idea about the size.
Oh, wow! It's got teeth!
It does look like a white shark in miniature!
They are very dangerous when they are...
trapped in small groups. At those moments, I would not dive with them.
There are many opinions and myths associated with the dangers of piranhas,
but the team were confident that they should be able to film the feeding frenzy safely.
Haroldo had recced this never-ending maze of river channels
a month previously, and thought he knew where to find the piranhas.
Peter it is highly experienced and has filmed many so-called dangers fish.
He at least remained sceptical about the risks of diving with piranhas.
How was that Pete? Well, interesting, different, no piranhas.
In fact, the main problems seem to be finding any piranhas in the first place
and the murky conditions underwater.
What's the vis like, Pete?
About three bad feet.
OK.
Three bad feet. Dusty, dirty, brown, dark.
Forget it. No. Forget it.
After two days of fruitless searching, tempers were beginning to fray.
This is so frustrating.
Stop it.
It's just...
a complete waste of time.
Well, these voracious monsters haven't turned up yet.
I don't believe the Hollywood stories.
We just haven't seen any piranhas and we're in hot piranha territory, so we're told.
I don't believe they exist.
MEN SPEAKING
Unfortunately, we have arrived at the wrong moment. There is too much water around here.
Piranhas are far away from the main stream, where the water is clear.
We must find another place.
Resorting to a spotter plane, they surveyed vast tracts of wetland
looking for pools of clean water and potential piranha habitat.
Back on the river and it was beginning to feel more like piranha country.
These fish are part of the staple diet here.
But sometimes dinner bites back.
After several minutes, she thought the piranha was dead
and she was removing the fish from the boat and the fish got her.
The big bite here.
He was just removing the hook from another piranha and approach the second one
that was supposed to be dead on the boat, and this one took a bite here.
They are very fast.
Like biting machines.
A single piranha bite is one thing, but what about a hungry shoal underwater?
I would advise you to not go further away under the vegetation, where it is very dark,
far from the mainstream.
Not...for a long time because they are approaching you,
circling,
and they come, curiously... and even try to bite.
At last, Peter was diving with piranhas,
but far from being any danger, they appeared to shy away from him.
They just go further and further and further into the dark, and... Very difficult.
Are they are avoiding you? They seem to be. I don't think they're used to divers.
Without a single shot in ten days, the pressure was building for Mark.
A change in tactic was called for and the team decided to try diving at night.
In this eerie underworld, they discovered shoals of fish
under the thick mats of weed, but the piranhas remained as elusive as ever.
Instead they found another predator, the spectacled caiman,
and decided to try to film these crocodilians the following morning.
Above three metres, crocodiles are considered too dangerous to dive with
but at just two metres, these caiman were the perfect subject.
Big enough to impress but too small to be a threat.
One came quite close, crawled over the top of the camera and chewed my hood.
Must have thought it was a purple fish or something!
Filming the caiman was a great morale booster for the team.
They returned to civilisation in high spirits, where piranhas still remain top of the menu.
Piranha soup. OK.
This is made especially from the head of the piranha, and it makes you strong.
You are going to become a macho Brazilian.
Macho man. Very strong.
Haroldo had received a tip-off from local fishermen the night before
of a promising piranha hot spot.
But time was running out.
Can you see any piranha? No, not yet.
At first it appeared to be another fisherman's tale, but suddenly their luck was about to change.
I can see the piranhas from here.
OK, good luck, Pete.
Fish activity had attracted good numbers of piranhas
out of the shadows, and they were starting to feed.
Yes!
Clear water,
good visibility and the piranhas in frenzy. This is what we want.
At last, Peter was in position to film unique wild piranha behaviour.
When they are in group...attacking, you must consider them dangerous.
Despite Haroldo's concerns, the piranhas were only interested in their fish prey.
As Peter expected, they never lived up to their frightening reputation
but he did develop a new respect for piranhas as highly effective group predators.
How was that? That went in about 20 seconds.
So you got a bit of respect for these guys now?
A number of those attacking en masse,
I believe they will strip a horse's head down in three minutes, yes. No problem.
You still got all your fingers? Yep.
Yep.