Planet Earth (2006): Season 1, Episode 3 - Fresh Water - full transcript

Although merely 3% of water on earth, fresh water plays an important part in the planet's weather and erosion. It is immensely important for all non-marine wildlife, which drinks fresh ...


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 vapour
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 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, 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 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'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.

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 are carrying
heavy loads of sediment

that stains their waters brown.

Lines of wildebeest are on their 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 vital source 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 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

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 twenty 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 bowls are courtship arenas.

Cichlids are caring parents.

Brooding young in the 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're 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 trenches 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 if 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's 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 fresh water

found in our planet's
lakes and rivers.

For five months of the year
it's 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 percent 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 tonnes 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
fresh water 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 a 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 dexterous 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 30 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 Victoria 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 spectacle 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.

The 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 rose-eared spoonbill is just one of the 650
bird species found in the Pantanal.

They nest alongside wood stocks
in colonies thousands strong.

Spectacle 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 thousand
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 Sundarbans.

These extraordinary forests
spring up throughout the tropics

in these tidal zones
where rivers meet the sea.

Crab-eating macaques
are mangrove specials.

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 river's journey.

Collectively they've
worn down mountains

and carried them to the sea.

And all along the way,

their fresh water has brought life
and abundance to planet Earth.