Only 3 percent 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 vapor
from the surface of the sea
is blown inland by wind.
On reaching mountains,
the moisture 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 a thousand meters.
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, its body flattened
to reduce drag,
has bushy gills to extract
oxygen from the current.
Black fly larvae anchor themselves
with the ring of hooks,
but if these become unstuck,
they're still held
by a silicon 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, world's largest amphibian,
almost two meters 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's spoilt for choice.
This Canadian bear is very special -
he's 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 the upland rivers
to shape the landscape
is greater than any other stage
in a river's life.
Driven by gravity,
they're the most erosive forces
on the planet.
For the past 5 million years
Arizona's Colorado river
has eaten away at the desert's sandstone
to create a gigantic canyon.
It's over a mile deep
and at its widest
it's 17 miles across.
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