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[narrator] Just 50 years ago,
we finally ventured to the moon.
For the very first time,
we looked back at our own planet.
Since then, the human population has more than doubled.
This series will celebrate the natural wonders that remain
and reveal what we must preserve
to ensure people and nature thrive.
Fresh water.
Everything that lives on land, animal or plant,
depends upon it.
Yet only one percent of it is within reach.
The desert of central Australia.
One of the hottest, driest places on Earth.
Virtually nothing can live here for any length of time.
Yet once a decade, this vast, empty desert is transformed.
For that to happen, a chain reaction has to be triggered
two thousand kilometers to the north.
There, each year, the moisture-laden clouds of the monsoon
begin to build. [thunder rumbling]
Eventually they burst, and the process begins.
Riverbeds that have been dry for years suddenly fill.
[birdsong]
The torrents join together and race towards the interior
and the lowest land on the continent.
Here, they flood over the desert and create Australia's largest lake,
Kati Thanda, Lake Eyre.
Huge numbers of fish swim down these wide waterways
and into the growing lake.
Pelicans arrive from Australia's coasts, hundreds of kilometers away.
Many will only see the lake fill once in their entire lives,
so how they know the lake has formed, and in which direction to reach it,
is still a mystery.
[pelicans cawing]
These new waters now contain so much food that the birds start to breed.
But the clock is ticking.
The pelicans feed...
and feed...
and feed.
The chicks must grow quickly,
for they have to be strong enough to leave within a matter of weeks.
But time is short,
for the parents will only be able to find food
while the water remains.
The young pelicans set off on their first long journey.
It will be a demanding one, to the coast,
and the nearest is 500 kilometers away.
The lake will soon dry,
and water may not return here for another decade.
This boom to bust transformation is an exceptional event.
But everywhere, the availability of fresh water
is becoming increasingly unpredictable and uncertain.
Much of the planet's fresh water, however, is locked away.
Almost two-thirds of it lies frozen around the poles.
This ice is several kilometers thick
and may have been lying here for millions of years.
Every summer, some of it melts
and carves its way into the heart of the glaciers.
These great caves are beautiful and romantic,
but they're also dangerous places, for glaciers are always on the move.
[glacier creaking] Even away from the poles,
much of the land's fresh water freezes each winter.
But when spring arrives, this vast snowy reservoir melts
and a great journey begins.
Racing down the steep mountain slopes,
the ice-cold waters collect a life-giving ingredient...
oxygen.
Here, on the rivers of the Andes in South America,
there is a living to be made
for those that can cope with the powerful currents.
And torrent ducks can.
[ducks squawking]
These chilly headwaters may be oxygen-rich,
but they contain few nutrients.
The torrent ducks collect what little food there is
from below the surface.
Stonefly and mayfly larvae have gills,
with which they extract oxygen from the water.
Their flattened bodies resist the relentless pull of the current.
Black fly larvae.
One of the ducks' favorite prey.
Their specialized mouthparts filter out the tiny particles of food
as they race by.
Hooks at the rear end anchor them to the rocks,
but the current is sometimes irresistible.
However, they have a special safety line, with which they can pull themselves back.
Every year, visitors come to these rushing, oxygen-rich waters.
Salmon.
They have spent most of their lives in the Pacific Ocean.
Now, fully grown, they're returning to the particular rivers in North America
where they will now lay their eggs.
Salmon have an extraordinary ability to leap up waterfalls,
but even they cannot, unaided, cross the dams that we have built.
Today, Pacific salmon number less than one percent of the numbers they used to,
and that's causing problems for many other animals.
Alaskan brown bears wait for them at the waterfalls.
Without these fish,
the bears cannot build up the fat reserves they need
to sustain themselves through their long winter hibernation.
There is fierce competition for the best fishing spots.
[growling] [gulls cawing]
Where water flows over hard rock, it collects few nutrients,
so few plants can grow in it.
Here, in South America, however,
this plant, Macarenia, manages to flourish.
For a few months each year,
when the water level is low enough for sunlight to reach the bottom,
the Macarenia bursts into bloom.
This is the Caño Cristales, Colombia's rainbow river.
Sometimes, however, water disappears underground,
beyond the reach of light,
and there, no plants can live.
Thirty percent of the planet's fresh water lies beneath the surface of the land,
either within the substance of porous rocks
or as subterranean lakes and rivers.
Made slightly acid by rain,
it slowly dissolves limestone, creating great caves.
A labyrinth of such passages and chambers underlies much of the state of Florida.
For the most part, they're barren.
But where the water comes to the surface, it's full of life.
Fish are abundant.
And so are fish eaters.
Otters.
All over the state, fresh water bubbles to the surface
from the greatest concentration of springs on Earth.
They feed rivers and pools, in which all kinds of life flourish,
including one of Florida's specialities...
manatees.
Many spend the summer in the sea,
but when winter approaches, they swim up the rivers,
which are relatively warm.
And there they graze on an abundance of freshwater plants.
But human beings are now taking so much water from these springs,
and polluting many of the others,
that the manatees are losing their winter homes.
Rivers, being comparatively shallow, warm quickly,
and in spring, across Europe,
the rising temperatures trigger a sudden surge of life.
[tweets]
On Hungary's Tisza River, giant mayfly are starting to emerge.
For three years, they've lived underwater as larvae.
Now, in just three hours,
millions of the winged adults dance together and mate before they die.
This extraordinary spectacle was once common in Eastern Europe,
but so many rivers now have stabilized banks
and are badly polluted
that the mayflies have largely disappeared.
But when the rivers are clean, wildlife is quick to return.
The kingfisher, the most glorious of divers.
The osprey, the most skillful of graspers.
Iguazu, on the frontier between Brazil and Argentina.
These are the largest waterfalls on the planet.
Thousands of tons of fresh water thunder over them every second.
Much of Iguazu's water comes from the Amazon rainforest,
a thousand kilometers away.
There, it rose as vapor from the surface of the jungle canopy.
A single tree can give off a thousand liters a day.
As the vapor rises into the sky, it condenses into clouds.
Twenty billion tons of water leave the forest each day,
more than travels down the Amazon River itself.
If the rainforest is destroyed,
this life-giving cycle will be broken.
As the clouds travel across the continent, they shed their water,
irrigating farmland and forest alike.
And on the plains of Brazil,
they create the largest tropical wetland on Earth,
the Pantanal.
Each year, however, seasonal changes reduce the river's flow,
and the Pantanal shrinks to just a few river channels.
This suits the top predator very well.
The jaguar.
It's a competent swimmer, but in water,
it can't make the killing pounce which makes it such a fearsome hunter.
[mewls]
Now, in the dry season,
the banks can get somewhat crowded.
But the jaguar has spotted prey on the river's edge.
Capybara.
It must get close to be successful.
Two capybara incautiously are standing in the shallows.
They have seen one another.
Which will run first?
[barks]
Farther along the river, dense vegetation provides better cover,
but the bank here is quite high.
Capybara have acute hearing.
-One noisy footfall... -[branch snaps]
...and the chance is lost. Another failure.
[barks]
Perhaps it's time to try a different prey.
Tackling one of these would be risky,
but the jaguar is really hungry.
If a jaguar is to catch a caiman,
it must bite its neck and then hold on to prevent the caiman striking back.
It has to get into a position directly above its prey.
This is dangerous.
The caiman rolls to try and drown the jaguar.
Predator and prey seem evenly matched.
The jaguar won't let go.
After 20 minutes, and near to exhaustion, the jaguar wins.
Sometimes, a river's downward journey is interrupted by lakes.
Together, they contain 40 times more water than all the world's rivers combined.
Africa's Lake Tanganyika
holds almost a fifth of all accessible fresh water on Earth.
But, considering its great size, Tanganyika contains little life.
It's almost a kilometer and a half deep,
but at the bottom the water barely moves and there is no oxygen.
It's only close to the surface, in its top 150 meters,
that the water contains enough oxygen for life to exist.
But here, it flourishes in abundance.
Two hundred and fifty species of cichlid fish have evolved here,
many of which are found nowhere else.
Competition in these crowded waters is intense.
A male callipterus cichlid collects shells.
The more shells a male has, the more females he will attract.
And this one is doing very well.
His neighbor has a rather smaller mound.
And the neighbor is a thief.
As soon as he turns his back,
the thief swoops in...
and steals a shell.
The hardworking owner of the larger mound doesn't seem to notice.
So, the thief commits the crime again...
and again...
until he has built the largest mound.
The shells are not just for display.
They will be used by the females as cradles.
One arrives.
She's tiny, only a tenth of his size.
She's so small, she can slip inside a shell.
There, she lays her eggs, and the male quickly fertilizes them.
She will then stay inside protecting them for up to a fortnight until they hatch.
The emperor,
the largest of all the cichlids in Tanganyika.
At almost a meter long, this female must raise her young in the open. Guarding them is therefore a full-time job for both parents.
But the future for all these fish is uncertain.
As global temperatures rise, Lake Tanganyika is warming.
Its waters are no longer mixing as well as they once did,
so the top oxygenated layer is reducing.
The Mekong River in Southeast Asia.
Four thousand kilometers long and with the widest falls anywhere.
Today, over 60 million people depend upon it for their livelihood.
The monsoon rains create such a colossal surge of water
that the falls themselves almost disappear.
The water is loaded with sediment,
collected during the Mekong's long journey from the Tibetan Plateau.
Even before the flood, the water covers a vast area of land.
These exposed roots are evidence
of the great rise in water level that is to come.
When the main flood does arrive,
the trees are submerged up to their branches.
For a few months, the floodwaters create the planet's greatest breeding grounds
for freshwater fish.
One species has a particularly ingenious solution
to the problems of living in shallow, oxygen-poor water.
The Siamese fighting fish.
The male breathes by gulping air from the surface,
and during the breeding season
he uses that ability to build a raft of bubbles.
Day after day he labors.
A female, waiting nearby, rises to inspect the raft.
They wrap themselves around one another in a tender embrace.
This union encourages her to release her eggs.
As they sink downwards, the male fertilizes them.
Both carefully collect them,
and then blow them, one by one, into the bubble nest.
Oxygen is scarce in these stagnant waters,
but the eggs will get enough from the bubbles
to allow them to develop.
The climax of the flood is still to come.
Eventually, so much water surges down the Mekong
that the Tonlé Sap Lake expands to five times its dry-season size.
Vast numbers of fish now swim into these new feeding grounds.
People have harvested this seasonal event for millennia.
They set nets across half of the river,
leaving the other half free
for the rest of the fish to swim on and breed.
The Mekong, in fact, supports the largest inland fishery in the world.
One-fifth of all the freshwater fish caught by people worldwide
comes from this one river system.
But the future of the Mekong,
like that of so many other rivers around the world,
is increasingly at risk.
We have changed the natural flow
of more than two-thirds of the planet's longest rivers
by, amongst other things, building dams across them.
So now, many rivers across the world no longer flow.
Here in East Africa, in Ruaha, Tanzania,
these elephants are searching for water.
Each needs to drink 200 liters every day, and there doesn't seem to be any here.
But the elephants know that baobab wood contains a lot of moisture.
And in an emergency, they eat it in great quantities.
Lions also need water.
And conveniently for the lions, water is where their prey will gather.
So both predators and prey head for the rivers.
Until 30 years ago,
rivers in this part of Africa never ran dry.
Now, agriculture upstream is taking great quantities,
and during the dry season, the rivers shrink into isolated pools.
Hippos rely on flowing water to keep themselves cool during the day,
but now they have to make do with mud.
As the water level falls still further, they cram together.
Tempers begin to fray.
[roaring]
Each day, the mud pools shrink further, and the hippos' plight worsens.
Buffalo, in the urgent search for water.
The lions are already here at this water hole.
However, the buffalo are driven on by their desperate need for fresh water.
They need to drink every day.
Every drink is now a risk,
but the buffalo have no choice.
As the drought continues, the buffalo begin to weaken.
The odds are changing, in the lions' favor.
The elephants have reached their river.
Nothing else is here because it's dry.
But elephants can find water where others can't.
They use their trunks to dig holes in the sand of the riverbed.
The extraordinary sense of smell
that enables them to detect open water from kilometers away
also helps them to locate places underground
where it lies closest to the surface.
In severe droughts, the wells they dig can be their lifeline.
The hardships of the dry season have always been part of life
on East Africa's plains,
but as the planet warms,
and we ourselves take so much water for our own purposes,
the droughts are becoming more frequent and more severe.
The Platte River, in Nebraska, North America.
Each year, sandhill cranes arrive here as they travel north across America
on one of the last great migrations made by any animal.
It's one of their crucial staging posts.
The river once flooded the prairie for a mile in all directions.
This was a perfect place for them to feed and rest.
Now, we have dammed the river
and taken so much of its water for our own use
that there is little space left for the cranes.
But conservationists now manage the river's flow in such a way
that it still creates the sandbanks the cranes need.
We are not alone in our need for water,
but we have the ability to ensure the fresh waters of the world do flow,
and we alone can determine how they are shared.
Please visit ourplanet.com to discover what we need to do now
to ensure fresh water keeps flowing.
♪ I can hear the whole world Singing together ♪
♪ I can hear the whole world Say it's now or never ♪
♪ 'Cause it's not too late If we change our ways ♪
♪ And connect the dots to our problems ♪
♪ I can hear the whole world Say we're in this together ♪