Fresh Water Planet Earth


Fresh Water

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Only 3% of the water on our planet is fresh.

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Yet these precious waters are rich with surprise.

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All life on land is ultimately dependent upon fresh water.

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The mysterious tepuis of Venezuela.

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Isolated mountain plateaus rising high above the jungle.

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This was the inspiration for Arthur Conan Doyle's Lost World,

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an imagined prehistoric land.

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Here, strange towers of sandstone have been sculptured

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over the millennia by battering wind and torrential rain.

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Moisture, rising as water vapour from the surface of the sea, is blown inland by wind.

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On reaching mountains, the moist air is forced upwards and, as it cools,

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it condenses into cloud and finally rain, the source of all fresh water.

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There is a tropical downpour here almost every day of the year.

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Fresh water's journey starts here, high in the mountains.

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Growing from humble streams to mighty rivers, it will travel hundreds of miles to the sea.

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Angel Falls, the highest waterfall in the world.

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Its waters drop unbroken for almost 1,000 metres.

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Such is the height of these falls

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that long before the water reaches the base in the Devil's Canyon,

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it's blown away as a fine mist.

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In their upper reaches, mountain streams are full of energy.

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Streams join to form rivers, building in power, creating rapids.

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The water here is cold, low in nutrients but high in oxygen.

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The few creatures that live in the torrent have to hang on for dear life.

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Invertebrates dominate these upper reaches.

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The hellgrammite, it's body flattened to reduce drag,

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has bushy gills to extract oxygen from the current.

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Blackfly larvae anchor themselves with a ring of hooks.

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But if these become unstuck, they are still held by a silken safety line.

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There are advantages to life in the fast stream.

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Bamboo shrimps can just sit and sift out passing particles with their fan-like forearms.

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Usually these mountain streams only provide enough food for small animals to survive.

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But with the spring melt here in Japan, monsters stir in their dens.

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Giant salamanders, the world's largest amphibian, almost two metres long.

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They're the only large predator in these icy waters.

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They begin their hunt at night.

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These salamanders have an exceptionally slow metabolism.

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Living up to 80 years, they grow into giants.

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The fish they hunt are scarce, and salamanders have poor eyesight.

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But sensory nodes on their head and body detect the slightest changes in water pressure.

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Free from competition, these giants can dine alone.

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Pickings are usually thin for the salamanders.

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But every year some of the world's high rivers are crowded by millions of visitors.

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The salmon have arrived.

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This is the world's largest fresh-water fish migration.

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Across the northern hemisphere, salmon returning from the ocean to their spawning grounds

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battle their way for hundreds of miles upstream.

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Up here there are fewer predators to eat their eggs and fry.

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A grizzly bear.

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From famine to feast, he is spoilt for choice.

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This Canadian bear is very special.

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He has learnt to dive for his dinner.

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But catching salmon in deep water is not that easy, and the cubs have lots to learn.

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The annual arrival of spawning salmon

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brings huge quantities of food into these high rivers that normally struggle to support much life.

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Although relatively lifeless, the power of these upland rivers to shape the landscape

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is greater than any other stage in a river's life.

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Driven by gravity, they are the most erosive forces on the planet.

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For the past five million years, Arizona's Colorado River has eaten away at the desert sandstone

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to create a gigantic canyon.

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It's over a mile deep and at its widest, it's 17 miles across.

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The Grand Canyon.

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This river has cut the world's longest canyon system.

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A 1,000 mile scar, clearly visible from space.

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As rivers leave the mountains behind, they gradually warm and begin to support more life.

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Indian rivers are home to the world's most social otter.

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Smooth-coated otters form family groups up to 17 strong.

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Group rubbing not only refreshes their coats but strengthens social bonds.

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When it comes to fishing, there is real strength in numbers.

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Fishing practice begins when the cubs are four months old.

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Only the adults have the speed and agility needed to make a catch.

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Adults share their catches with their squabbling cubs.

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Most otters are solitary,

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but these rich warm waters can support large family groups,

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and even bigger predators.

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Mugger crocodiles, four metres long, could easily take a single otter.

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But confident in their gangs,

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the otters will actively harass these great reptiles.

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Team play wins the day.

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The Mara River, snaking across the plains of East Africa.

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As the land flattens out, rivers slow down and lose their destructive power.

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Now they're carrying heavy loads of sediment that stains their waters brown.

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Lines of wildebeest are on the march.

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Each year, nearly two million animals

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migrate across the Serengeti plains in search of fresh green pastures.

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For these thirsty herds, the rivers are not only a vitalsource of drinking water

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but also dangerous obstacles.

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This is one of the largest concentrations of Nile crocodiles in Africa,

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giants that grow over five metres long.

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From memory, the crocodiles know the wildebeest are coming, and gather in anticipation.

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The crocodile's jaws snap tight, like a steel trap.

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Once they have a hold they never let go.

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It took over an hour to drown this full grown bull.

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To surprise their prey, the crocodiles must strike with lightning speed.

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Here, only the narrowest line

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separates life from death.

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Most rivers drain into the sea, but some end their journey in vast lakes.

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Worldwide, lakes hold 20 times more fresh water than all the rivers.

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The East African Rift Valley holds three of the world's largest,

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Malawi, Tanganyika and Victoria.

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Lake Malawi, the smallest of the three, is still bigger than Wales.

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Its tropical waters teem with more fish species than any other lake.

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There are 850 different cichlids alone,

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all of which evolved from just one single ancestor

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isolated here thousands of years ago.

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These two-metre wide craters are fish-made.

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Fastidiously maintained by the males, these bowers are courtship arenas.

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Cichlids are caring parents.

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Brooding young in their mouth is a very effective way of protecting them.

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This lake can be a dangerous place.

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After dark, predatory dolphin fish emerge from their daytime lairs among the rocks.

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Like packs of sharks, they are on the prowl for sleeping cichlids.

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In the darkness,

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these electric fish hunt by detecting distortions in the electric field they create

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around their bodies.

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Any cichlid that ventures out will be snapped up.

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The floor of Lake Malawi drops 700 metres into an abyss.

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Here in this dead zone, the larvae of lake fly midges hide out away from predators.

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In the rainy season, they balloon up to the surface and undergo a magical transformation.

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At dawn, the first adult midges start to break out.

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Soon, millions upon millions of newly hatched lake flies are taking to the wing.

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Early explorers told tales of lakes that smoked, as if on fire.

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But these spiralling columns, hundreds of metres high, are mating flies.

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Once the flies have mated, they will all drop to the water surface, release their eggs and die.

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Malawi may look like an inland sea,

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but it is dwarfed by the world's largest lake,

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Baikal in eastern Siberia.

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400 miles long and over a mile deep,

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Baikal contains one fifth of all the freshwater

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found in our planet's lakes and rivers.

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For five months of the year, it is sealed by an ice sheet over a metre thick.

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Baikal is the oldest lake in the world

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and despite the harsh conditions, life flourishes here in isolation.

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80% of its species are found nowhere else on Earth,

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including the world's only fresh water seal.

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With this seal and its marine-like forests of sponges,

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Baikal seems more like an ocean than a lake.

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There are shrimp-like crustaceans, giant amphipods as large as mice.

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They are the key scavengers in this lake.

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The water here is just too cold for the bacteria that normally decompose the dead.

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Most rivers do not end in lakes but continue their journey to the sea.

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The planet's indisputable super-river is the Amazon.

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It carries as much water as the next top-ten biggest rivers combined.

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Rising in the Peruvian Andes, its main trunk flows eastwards across Brazil.

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On its way, the system drains a third of South America.

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Eventually over 4,000 miles from its source it empties into the Atlantic Ocean.

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The Amazon transports a billion tons of sediment a year, sediment clearly visible

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at the "mixing of the waters" - where one massive tributary, the Rio Negro, flows into the main river.

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Its waters are wonderfully rich.

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To date, over 3,000 species of their fish have been described,

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more than in the whole of the Atlantic Ocean.

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The Amazon is so large and rich in fish that it can support freshwater dolphins.

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These botos are huge, two-and-a-half metres long.

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In these murky waters, they rely on sonar to navigate and hunt.

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They work together to drive shoals of fish into the shallows.

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Botos are highly social, and in the breeding season there is stiff competition for mates.

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The males hold court in an unique way.

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They pick up rocks in their jaws and flaunt them to their attending females.

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Maybe each male is trying to show how strong and dextrous he is

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and that he therefore is the best father a female could have for her young.

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Successful displays lead to mating.

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Even for giant rivers like the Amazon

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the journey to the sea is not always smooth or uninterrupted.

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Iguassu Falls, on the border of Brazil and Argentina,

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is one of the widest waterfalls in the world, one-and-a-half miles across.

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In flood, 13 million litres of water spill over every second.

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All the world's great broad waterfalls -

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Victoria, Niagara and here Iguassu,

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are only found in the lower courses of their rivers.

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In their final stages, rivers broaden and flow wearily across their flat flood plains.

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Each wet season here in Brazil,

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the Parana river overflows its banks and floods an area the size of England.

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The Pantanal, the world's largest wetland.

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In these slow-flowing waters, aquatic plants flourish,

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like the Victorian giant water lily, with leaves two metres across.

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These underwater forests are nursery grounds for fish.

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Over 300 species breed here, including red-bellied piranha.

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And other predators, like the spectacled caiman.

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Ripening fig trees, overhanging the water's edge,

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provide welcome food for shoals of hungry fish.

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The commotion attracts dorado, known locally as the river tiger.

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They patrol the feeding shoals, looking for a chance to strike.

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And waiting in the wings, ready to pick off any injured fish, are the piranhas.

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A feeding frenzy quickly develops.

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Piranha can strip a fish to the bone in minutes.

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Great numbers of fish sustain vast flocks of water birds.

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The roseate spoonbill is just one of the 650 bird species found in the Pantanal.

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They nest alongside wood storks, in colonies thousands strong.

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Spectacled caiman linger below, waiting for a meal to fall out of the sky.

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When rivers finally reach the sea, they slow down, release their sediment and build deltas.

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In Bangladesh, the Ganges and Brahmaputra rivers join to form the world's biggest.

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Every year, almost 2,000 million tonnes of sediment,

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eroded from the Himalayas is delivered to the ocean.

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At the delta's mouth, the largest mangrove forest in the world, the Sunderbans.

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These extraordinary forests spring up throughout the tropics

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in these tidal zones where rivers meet the sea.

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Crab-eating macaques are mangrove specialists.

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In Indonesia,

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these monkeys have adopted a unique amphibious lifestyle.

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They fish out fallen food.

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The troop also uses the waters to cool off during the heat of the day.

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But the channels are also the playground for restless young macaques.

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Some of the young have even taken to underwater swimming.

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They can stay down for more than 30 seconds

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and appear to do this just for fun.

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Yet these swimming skills, acquired during play,

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will certainly be useful later in life in these flooded mangrove forests.

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In cooler climes, mud laid down in estuaries

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is colonised by salt-marsh grasses

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and form one of the most productive habitats on the planet.

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400,000 greater snow geese flock to the estuaries along the Atlantic coast of the United States

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to rest and refuel on their long migratory journeys.

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This is the end of the rivers' journey.

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Collectively they've worn down mountains and carried them to the sea.

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And all along the way, their fresh water has brought life in abundance

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to planet Earth.

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Filming piranhas in a feeding frenzy in the wild

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has rarely, if ever, been attempted

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and it was to prove the freshwater team's greatest challenge.

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Welcome to the piranhas' country.

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Arriving in the Pantanal

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with over a tonne of dive and camera equipment,

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producer Mark Brownlow and his team were heading into uncharted waters which had never been dived before.

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The piranha lives everywhere. It is the most common fish here.

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I have a gift for Peter. This will give a good idea about the size.

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Oh, wow! It's got teeth!

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It does look like a white shark in miniature!

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They are very dangerous when they are...

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trapped in small groups. At those moments, I would not dive with them.

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There are many opinions and myths associated with the dangers of piranhas,

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but the team were confident that they should be able to film the feeding frenzy safely.

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Haroldo had recced this never-ending maze of river channels

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a month previously, and thought he knew where to find the piranhas.

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Peter it is highly experienced and has filmed many so-called dangers fish.

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He at least remained sceptical about the risks of diving with piranhas.

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-How was that Pete?

-Well, interesting, different, no piranhas.

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In fact, the main problems seem to be finding any piranhas in the first place

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and the murky conditions underwater.

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What's the vis like, Pete?

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About three bad feet.

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OK.

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Three bad feet. Dusty, dirty, brown, dark.

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-Forget it.

-No.

-Forget it.

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After two days of fruitless searching, tempers were beginning to fray.

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This is so frustrating.

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Stop it.

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It's just...

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a complete waste of time.

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Well, these voracious monsters haven't turned up yet.

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I don't believe the Hollywood stories.

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We just haven't seen any piranhas and we're in hot piranha territory, so we're told.

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I don't believe they exist.

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MEN SPEAKING

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Unfortunately, we have arrived at the wrong moment. There is too much water around here.

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Piranhas are far away from the main stream, where the water is clear.

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We must find another place.

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Resorting to a spotter plane, they surveyed vast tracts of wetland

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looking for pools of clean water and potential piranha habitat.

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Back on the river and it was beginning to feel more like piranha country.

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These fish are part of the staple diet here.

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But sometimes dinner bites back.

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After several minutes, she thought the piranha was dead

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and she was removing the fish from the boat and the fish got her.

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The big bite here.

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He was just removing the hook from another piranha and approach the second one

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that was supposed to be dead on the boat, and this one took a bite here.

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They are very fast.

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Like biting machines.

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A single piranha bite is one thing, but what about a hungry shoal underwater?

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I would advise you to not go further away under the vegetation, where it is very dark,

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far from the mainstream.

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Not...for a long time because they are approaching you,

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circling,

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and they come, curiously... and even try to bite.

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At last, Peter was diving with piranhas,

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but far from being any danger, they appeared to shy away from him.

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They just go further and further and further into the dark, and... Very difficult.

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-Are they are avoiding you?

-They seem to be. I don't think they're used to divers.

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Without a single shot in ten days, the pressure was building for Mark.

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A change in tactic was called for and the team decided to try diving at night.

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In this eerie underworld, they discovered shoals of fish

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under the thick mats of weed, but the piranhas remained as elusive as ever.

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Instead they found another predator, the spectacled caiman,

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and decided to try to film these crocodilians the following morning.

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Above three metres, crocodiles are considered too dangerous to dive with

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but at just two metres, these caiman were the perfect subject.

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Big enough to impress but too small to be a threat.

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One came quite close, crawled over the top of the camera and chewed my hood.

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Must have thought it was a purple fish or something!

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Filming the caiman was a great morale booster for the team.

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They returned to civilisation in high spirits, where piranhas still remain top of the menu.

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-Piranha soup.

-OK.

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This is made especially from the head of the piranha, and it makes you strong.

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You are going to become a macho Brazilian.

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Macho man. Very strong.

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Haroldo had received a tip-off from local fishermen the night before

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of a promising piranha hot spot.

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But time was running out.

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-Can you see any piranha?

-No, not yet.

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At first it appeared to be another fisherman's tale, but suddenly their luck was about to change.

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I can see the piranhas from here.

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OK, good luck, Pete.

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Fish activity had attracted good numbers of piranhas

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out of the shadows, and they were starting to feed.

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Yes!

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Clear water,

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good visibility and the piranhas in frenzy. This is what we want.

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At last, Peter was in position to film unique wild piranha behaviour.

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When they are in group...attacking, you must consider them dangerous.

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Despite Haroldo's concerns, the piranhas were only interested in their fish prey.

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As Peter expected, they never lived up to their frightening reputation

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but he did develop a new respect for piranhas as highly effective group predators.

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-How was that?

-That went in about 20 seconds.

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So you got a bit of respect for these guys now?

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A number of those attacking en masse,

0:57:390:57:41

I believe they will strip a horse's head down in three minutes, yes. No problem.

0:57:410:57:46

-You still got all your fingers?

-Yep.

0:57:460:57:49

Yep.

0:57:500:57:51

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