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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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00:00:54,080 --> 00:00:58,990
All life on land is ultimately
dependant upon fresh water.
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00:01:29,600 --> 00:01:32,710
The mysterious tepuis of Venezuela,
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isolated mountain plateaus
rising high above the jungle.
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00:01:48,560 --> 00:01:53,430
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 over the millennia
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by battering wind and torrential rain.
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00:02:23,280 --> 00:02:27,430
Moisture, rising as water vapour
from the surface of the sea,
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is blown inland by wind.
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00:02:42,200 --> 00:02:45,870
On reaching mountains,
the moist air is forced upwards
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00:02:45,960 --> 00:02:49,390
and as it cools, it condenses into cloud
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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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00:03:41,520 --> 00:03:44,670
Growing from humble streams to mighty rivers,
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it will travel hundreds of miles to the sea.
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00:04:25,040 --> 00:04:29,150
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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00:06:11,040 --> 00:06:15,510
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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00:06:21,200 --> 00:06:24,910
The hellgrammite,
its body flattened to reduce drag,
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has bushy gills to extract oxygen from the current.
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Black fly larvae anchor themselves
with a ring of hooks.
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But if these become unstuck,
they're 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
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with their fan-like forearms.
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Usually these mountain streams
only provide enough food
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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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00:07:49,520 --> 00:07:53,790
Giant salamanders, the world's largest amphibian,
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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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00:08:25,120 --> 00:08:29,470
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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00:09:16,240 --> 00:09:21,110
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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00:10:01,240 --> 00:10:05,590
This is the world's largest
freshwater fish migration.
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00:10:09,720 --> 00:10:11,550
Across the northern hemisphere,
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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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00:10:23,560 --> 00:10:27,910
Up here there are fewer predators
to eat their eggs and fry.
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00:10:55,320 --> 00:10:56,830
A grizzly bear.
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From famine to feast, he's spoilt for choice.
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00:11:10,640 --> 00:11:13,470
This Canadian bear is very special.
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He's learnt to dive for his dinner.
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00:11:30,840 --> 00:11:34,710
But catching salmon in deep water
is not that easy,
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and the cubs have lots to learn.
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The annual arrival of spawning salmon brings
huge quantities of food into these high rivers
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that normally struggle to support much life.
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00:12:35,680 --> 00:12:37,790
Although relatively lifeless,
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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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00:12:46,960 --> 00:12:51,670
Driven by gravity,
they're the most erosive forces on the planet.
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00:12:56,200 --> 00:12:58,710
For the past five million years,
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00:12:58,800 --> 00:13:03,590
Arizona's Colorado River
has eaten away at the desert sandstone
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00:13:03,680 --> 00:13:06,430
to create a gigantic canyon.
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00:13:17,120 --> 00:13:19,150
It's over a mile deep
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and at its widest, it's 17 miles across.
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The Grand Canyon.
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00:13:58,080 --> 00:14:02,670
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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00:14:33,280 --> 00:14:36,070
As rivers leave the mountains behind,
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they gradually warm
and begin to support more life.
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00:14:49,000 --> 00:14:53,630
Indian rivers are home
to the world's most social otter.
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00:14:54,880 --> 00:14:59,630
Smooth-coated otters
form family groups up to 17 strong.
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00:15:10,760 --> 00:15:14,470
Group rubbing not only refreshes their coats,
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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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00:17:04,720 --> 00:17:06,950
Most otters are solitary,
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00:17:07,040 --> 00:17:11,510
but these rich, warm waters
can support large family groups
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and even bigger predators.
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00:17:33,440 --> 00:17:38,710
Mugger crocodiles, four metres long,
could easily take a single otter.
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00:18:04,480 --> 00:18:06,950
But confident in their gangs,
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the otters will actively harass these great reptiles.
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00:18:28,040 --> 00:18:31,030
Team play wins the day.
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00:18:41,400 --> 00:18:46,110
The Mara River,
snaking across the plains of East Africa.
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00:18:48,520 --> 00:18:53,510
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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00:19:13,200 --> 00:19:16,270
Lines of wildebeest are on the march.
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00:19:21,320 --> 00:19:24,710
Each year, nearly two million animals migrate
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across the Serengeti Plains
in search of fresh, green pastures.
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00:19:30,040 --> 00:19:31,670
For these thirsty herds,
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the rivers are not only
a vital source 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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00:20:22,680 --> 00:20:26,150
From memory, the crocodiles
know the wildebeest are coming
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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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00:22:03,400 --> 00:22:08,830
To surprise their prey,
crocodiles must strike with lightning speed.
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Here, only the narrowest line
separates life from death.
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Most rivers drain into the sea,
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00:23:17,520 --> 00:23:21,590
but some end their journey in vast lakes.
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00:23:24,600 --> 00:23:30,230
Worldwide, lakes hold 20 times more fresh water
than all the rivers.
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00:23:33,000 --> 00:23:37,670
The East African Rift Valley
holds three of the world's largest,
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Malawi, Tanganyika and Victoria.
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00:23:43,680 --> 00:23:48,510
Lake Malawi, the smallest of the three,
is still bigger than Wales.
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00:24:01,520 --> 00:24:06,990
Its tropical waters teem with more fish species
than any other lake.
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00:24:07,960 --> 00:24:11,270
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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00:24:32,280 --> 00:24:36,350
These two-metre wide craters are fish-made.
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00:24:46,080 --> 00:24:52,030
Fastidiously maintained by the males,
these bowers are courtship arenas.
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Cichlids are caring parents.
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00:25:11,520 --> 00:25:15,990
Brooding young in the mouth
is a very effective way of protecting them.
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00:25:17,880 --> 00:25:20,550
This lake can be a dangerous place.
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00:25:33,080 --> 00:25:39,030
After dark, predatory dolphin fish emerge
from their daytime lairs among the rocks.
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00:25:44,480 --> 00:25:49,390
Like packs of sharks,
they're on the prowl for sleeping cichlids.
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00:25:56,680 --> 00:26:01,750
In the darkness, these electric fish
hunt by detecting distortions
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in the electric field
they create around their bodies.
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Any cichlid that ventures out will be snapped up.
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00:26:48,560 --> 00:26:54,550
The floor of Lake Malawi
drops 700 metres into an abyss.
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Here in this dead zone
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the larvae of lake fly midges
hide out away from predators.
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00:27:11,800 --> 00:27:17,710
In the rainy season, they balloon up to the surface
and undergo a magical transformation.
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00:27:27,400 --> 00:27:31,350
At dawn, the first adult midges start to break out.
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00:27:35,840 --> 00:27:39,870
Soon, millions upon millions
of newly-hatched lake flies
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are taking to the wing.
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00:27:51,960 --> 00:27:56,870
Early explorers told tales of lakes
that smoked as if on fire.
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00:27:59,000 --> 00:28:02,670
But these spiralling columns,
hundreds of metres high,
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are mating flies.
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00:28:18,720 --> 00:28:22,870
Once the flies have mated,
they will all drop to the water surface,
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release their eggs and die.
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00:28:35,280 --> 00:28:38,350
Malawi may look like an inland sea,
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00:28:38,440 --> 00:28:42,230
but it's dwarfed by the world's largest lake.
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00:28:43,600 --> 00:28:46,630
Baikal in eastern Siberia.
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00:28:57,280 --> 00:29:00,110
Four hundred miles long and over a mile deep,
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00:29:00,240 --> 00:29:06,310
Baikal contains one-fifth of all the fresh water
found in our planet's lakes and rivers.
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00:29:09,720 --> 00:29:15,310
For five months of the year,
it's sealed by an ice sheet over a metre thick.
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00:29:30,840 --> 00:29:33,590
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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00:29:40,760 --> 00:29:44,350
80% of its species are found
nowhere else on Earth,
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including the world's only freshwater seal.
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00:29:55,000 --> 00:29:58,870
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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00:30:21,240 --> 00:30:27,070
There are shrimp-like crustaceans,
giant amphipods as large as mice.
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00:30:33,160 --> 00:30:36,150
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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00:30:55,840 --> 00:31:01,710
Most rivers do not end in lakes
but continue their journey to the sea.
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00:31:07,080 --> 00:31:11,470
The planet's indisputable super river
is the Amazon.
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00:31:13,840 --> 00:31:19,590
It carries as much water
as the next top 10 biggest rivers combined.
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00:31:22,840 --> 00:31:28,590
Rising in the Peruvian Andes,
its main trunk flows eastwards across Brazil.
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00:31:29,040 --> 00:31:33,270
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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00:31:49,120 --> 00:31:53,350
The Amazon transports a billion tonnes
of sediment a year,
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sediment clearly visible
at the mixing of the waters,
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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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00:32:11,320 --> 00:32:15,510
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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00:32:46,360 --> 00:32:52,270
The Amazon is so large and rich in fish
that it can support freshwater dolphins.
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00:32:52,600 --> 00:32:56,550
These botos are huge, 2.5 metres long.
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00:32:59,960 --> 00:33:04,550
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
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and in the breeding season,
there is stiff competition for mates.
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The males hold court in a 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 dexterous he is
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00:35:03,960 --> 00:35:08,590
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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00:36:13,320 --> 00:36:17,590
Iguaçú Falls,
on the border of Brazil and Argentina,
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is one of the widest waterfalls in the world,
1 .5 miles across.
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00:36:29,880 --> 00:36:35,110
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, Iguaçú,
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are only found in the lower courses of their rivers.
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In their final stages,
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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 Paraná river overflows its banks
and floods an area the size of England.
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00:37:59,120 --> 00:38:02,830
The Pantanal, the world's largest wetland.
194
00:38:10,160 --> 00:38:14,710
In these slow-flowing waters,
aquatic plants flourish,
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like the Victoria Giant Water Lily,
with leaves two-metres across.
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00:38:42,360 --> 00:38:46,630
These underwater forests
are nursery grounds for fish.
197
00:38:48,720 --> 00:38:53,510
Over 300 species breed here,
including red-bellied piranha.
198
00:38:58,320 --> 00:39:01,990
And other predators, like the spectacled caiman.
199
00:39:28,320 --> 00:39:35,070
Ripening fig trees, overhanging the water's edge,
provide welcome food for shoals of hungry fish.
200
00:39:42,320 --> 00:39:48,270
The commotion attracts dorado,
known locally as the river tiger.
201
00:39:55,720 --> 00:40:00,670
They patrol the feeding shoals
looking for a chance to strike.
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00:40:37,440 --> 00:40:42,030
And waiting in the wings,
ready to pick off any injured fish,
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are the piranhas.
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A feeding frenzy quickly develops.
205
00:41:16,400 --> 00:41:20,350
Piranha can strip a fish to the bone in minutes.
206
00:41:27,040 --> 00:41:32,870
Great numbers of fish
sustain vast flocks of water birds.
207
00:41:35,840 --> 00:41:40,830
The roseate spoonbill
is just one of the 650 bird species
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found in the Pantanal.
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They nest alongside woodstorks
in colonies thousands strong.
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00:42:23,160 --> 00:42:28,790
Spectacled caiman linger below,
waiting for a meal to fall out of the sky.
211
00:43:24,320 --> 00:43:26,510
When rivers finally reach the sea,
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they slow down,
release their sediment and build deltas.
213
00:43:32,880 --> 00:43:36,430
In Bangladesh,
the Ganges and Brahmaputra rivers
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join to form the world's biggest.
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00:43:41,640 --> 00:43:47,870
Every year, almost 2,000 million tonnes
of sediment eroded from the Himalayas
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is delivered to the ocean.
217
00:43:54,920 --> 00:43:59,230
At the delta's mouth,
the largest mangrove forest in the world,
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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.
221
00:44:25,000 --> 00:44:28,390
Crab-eating macaques are mangrove specialists.
222
00:44:32,680 --> 00:44:38,310
In Indonesia, these monkeys
have adopted a unique amphibious lifestyle.
223
00:44:46,680 --> 00:44:49,110
They fish out fallen food.
224
00:45:12,120 --> 00:45:17,110
The troop also uses the waters to cool off
during the heat of the day.
225
00:45:22,360 --> 00:45:27,030
But the channels are also the playground
for restless young macaques.
226
00:45:33,240 --> 00:45:37,150
Some of the young have even taken
to underwater swimming.
227
00:45:42,840 --> 00:45:48,550
They can stay down for more than 30 seconds
and appear to do this just for fun.
228
00:46:00,880 --> 00:46:04,790
Yet these swimming skills acquired during play
229
00:46:04,880 --> 00:46:09,830
will certainly be useful later in life
in these flooded mangrove forests.
230
00:46:18,600 --> 00:46:25,110
In cooler climes, mud laid down in estuaries
is colonised by salt marsh grasses,
231
00:46:25,360 --> 00:46:29,030
and form one of the most productive habitats
on the planet.
232
00:46:58,120 --> 00:47:02,350
Four hundred thousand greater snow geese
flock to the estuaries
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00:47:02,440 --> 00:47:05,230
along the Atlantic coast of the United States
234
00:47:05,320 --> 00:47:09,270
to rest and refuel on their long migratory journeys.
235
00:47:45,440 --> 00:47:48,750
This is the end of the rivers' journey.
236
00:47:48,840 --> 00:47:53,190
Collectively, they've worn down mountains
and carried them to the sea.
237
00:47:53,320 --> 00:47:54,870
And all along the way,
238
00:47:54,960 --> 00:47:59,150
their fresh water has brought life
in abundance to planet Earth.
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