All language subtitles for BBC.Wild.Africa.6of6.Lakes.and.Rivers.Xvid.AC3.www.mvgroup.org.ENG

Africa is a parched continent...

...where the driving force of life
is fresh water.

Often sparse - but sometimes torrential

water is an architect of landscapes...

and a catalyst for some of
the most dazzling wildlife spectacles.

This is the story of
Africa's most precious commodity...

and of the many enchanting worlds
it has created.

The source of all of Africa's fresh water
are rain-bearing clouds,

rising off the warm oceans
which surround the continent.

Washing over the land,
their destination is uncertain...

and ruled by fickle winds.

But it's Africa's high ground
the hills and mountains

which catch most of their precious cargo.

The contours of the land...

the troughs and valleys first channel
the flow of water...

Gathering in volume and strength,

water increasingly takes control...
carving its own path.

Victoria Falls in Zimbabwe...

the greatest single curtain of water
in the world...

little wonder, the local tribes call it
'the smoke that thunders.'

With thousands of streams now channelled
into one powerful river...

the waters become
their own natural architect.

Boulders hammer at the river bed...

making the Falls ever higher,
the gorges deeper.

This body of water has a name...
the Zambezi River.

As the land levels out,

the river becomes
a frontier of opportunity...

The waters are calmer... warmer...

rich with oxygen and dissolved minerals...
crucial ingredients for life.

And the fishing's good!

The reed cormorant is beautifully
streamlined to pursue catfish...

Fish is also the staple of
the local Tokaleya people.

From its source over
a thousand kilometres away,

the Zambezi waters are now tamed...

gentle and rich enough to support life.

The Zambezi is one of four major rivers

which originate
in equatorial Africa and branch out

like giant arteries
across the continent.

Clearly visible from space,

the Congo drains over 3 million square
kilometres of tropical rainforest.

The Nile is the world's longest river...

flowing almost 7000 kilometres
to the Mediterranean.

And the mighty Niger...

bringing life to
West Africa's Sahel desert.

Feeding these great rivers are
a myriad of tributaries...

branching like capillaries
across the face of Africa.

Tributaries yes - but by any standards
still great rivers.

Like the Luangwa, which feeds the Zambezi.

Winding its way from the high ground,

the Luangwa has slowed
and collected silt...

which it now sheds...
to form a near-desert landscape.

For land animals,

the river is one of the few places
to get a much-needed drink.

Here - as in most of Africa
the rains are sparse and unpredictable.

The drought can last 8 months or more...

the Luangwa a dwindling resource.

Though 57 million tonnes of rain falls
on the African continent every day,

as much as 80o/o of it is lost
by evaporation or absorbed by the ground...

so the rest is precious...

Such is the demand for water,

that all sorts of takers
crowd the riverbank...

assuming a temporary truce.

But quenching a thirst
is not without risk.

The Nile crocodile...
a creature older than Africa itself...

its hunting skills honed
over 200 million years.

Using extreme stealth,

the crocodile needs to get
within a metre of its prey.

Desperate to drink,
the buffalo seem blind to the danger.

...just too much
for a croc out of water...

...but they'll be another chance.

The dry season brings plenty of
opportunity for crocodiles,

but it's a real problem

for Africa's other large freshwater animal
the hippopotamus.

Hippos need deep water to protect
their skin from the harsh sun.

And when the river falls
to a critically low level,

the males become fired with aggression...

These brutal battles are all about
winning deep-water territory,

which the females prefer.

For the victors the rewards of deep water

and numerous females will be enormous...

The lives of hippos are ruled
by the ebb and flow of the seasons,

but these small savannah finches
known as "quelea"

are totally nomadic,

instinctively finding water
from hundreds of kilometres away.

Like locusts, they swarm in their millions,

forming flocks up to 4kms wide.

Quelea - like many birds
in subtropical Africa

breed when food and rainfall
are plentiful.

But here in Luangwa,
one spectacular bird does the opposite.

Carmine bee-eaters breed
at the hottest time of the year,

when the sandy banks of the river
are exposed by the low water.

He's not banging his head
against a brick wall

but excavating a nest chamber.

It's a yearly chore,

as the river is always
reshaping the banks.

The steepest cliffs are most in demand
because they're safest from predators.

Some bee-eaters will try anything
to get what they want...

But owning a nest doesn't
guarantee a mate...

she must also be seduced with a gift.

He offers her a bee to seal the bond.

In a crowded colony like this,
parasites and ticks are rife,

so carmine bee-eaters take time out
to burn them off in the sun.

But they can't afford to relax...

the racket of breeding birds
always attracts trouble.

Enter the dragon.

Monitor lizards are formidable scavengers
and competent swimmers

quite at ease along Africa's rivers.

The bee-eaters are powerless to stop
this determined egg thief.

But by breeding in huge numbers

only a small proportion of
the nests are raided.

And many of the eggs are out of reach.

It's not just monitor lizards
that the bee-eaters need to fear.

Along the banks of the Luangwa
is a far greater threat.

...the African fish eagle...

...also partial to birds.

For male hippos it's the drought
that can be a killer.

Under baking skies, those wounded and
exhausted from battle can easily succumb.

And waiting in the wings...
the patient undertaker.

Though their diet is usually small fish,

crocodiles can get by on
just one big meal a year...

...and a large male hippo carries
more than two tonnes of flesh.

A crocodile's stomach juices are
more acidic than any other animal

strong enough to digest every part of
the carcass - even hooves, bones and skin.

Despite their massive jaws,
crocodiles can't chew,

but they can tear off large chunks of
meat by gripping the carcass and spinning.

The largest crocs can gorge nearly half
a tonne of flesh.

Under such an assault the carcass
can vanish in a matter of hours.

Africa's rivers are vital lifelines,

bringing relief to the harshest of places,

yet they hold only a fraction of
the continent's fresh water.

Over the last 20 million years

Africa has been tearing apart
along the Great Rift Valley,

creating new basins which have
since filled with water.

The result is a string of giant lakes...

such as Tanganyika, Kivu... and Malawi.

Lake Malawi is an ocean of
permanent fresh water...

nearly a kilometre deep and 600 kms long.

The birth of this great lake brought
with it a rapid explosion of life.

More than 700 types of cichlid fish
have evolved from a single species

which first entered the lake
from nearby rivers.

Through competition for food and space,

each type of cichlid has developed
its own special habits.

Many feed on algae

each evolved to harvest different types
of rock face.

But not all cichlids are vegetarians.

Stalking the mid-water shoals is a fish
which is fast as lightning...

...the barracuda of Lake Malawi.

And lurking beneath,
the only fish in the world who plays dead.

This cichlid lures prey
by mimicking a rotting corpse.

In such a dangerous world,
young cichlids need cover.

Many Malawi mothers protect their brood
in their mouths.

It works fine until the youngsters
get too big...

When that happens,
these particular cichlids swim deep...

Fifty metres down
they find new child minders...

a pair of catfish.

The catfish already
have a large brood of their own,

yet they tolerate adopting
hundreds of young cichlids.

This remarkable behaviour is so new to
science that no one yet knows how

or why it has evolved.

Lake Malawi is a stable body of water,

where life is sheltered
from extremes of climate...

but the arrival of the rains
has a profound influence

on all its inhabitants.

Erupting from the lake surface,
billions of flies...

forming clouds 2 kms high and 5 kms wide.

No-one knows what triggers this event...

the cycle of the moon...

or maybe the hammering of raindrops
on water.

For the flies, the journey
from the lake bed is perilous...

Their larvae must ascend 40m...

running the gauntlet of a thousand mouths.

Even when they've reached
the breeding swarm,

the lake flies aren't safe...

they're a feast for swallows,
swifts and martins...

fattening up before
their long migration to Europe.

After mating the females lay their eggs
on the lake surface...

and then they die...
all within a few days.

Another bonanza for cichlids.

But feeding at the lake surface
is dicing with death.

The pied kingfisher...
an open-water marksman...

Pied kingfishers are
the largest kingfishers in Africa,

able to fly 20 kms offshore to hunt.

Lake Malawi is so productive that nearly
a quarter of a million people

make their living from it.

Seventy per cent of all the protein

in the local diet comes directly
from fish.

With their abundant riches
and endless fresh water,

Africa's Great Lakes are like vast oases
in a predominantly dry continent.

But their influence stretches
far beyond their shores.

During the rainy season
the level of the Great Lakes

can rise by over three metres.

Spread over an area
twice the size of Ireland

this represents trillions of
tonnes of extra water.

The swollen lakes can't hold
all the surplus water.

It floods into surrounding rivers
which overspill their banks...

priming new types of water world...
Africa's wetlands.

Each year the Chambeshi river inundates
10,000 sq kms of Zambia...

turning it into the vast Bengweulu swamp.

Its waters are warm and shallow...

thick with nutrients...
and bursting with life.

Mobility is the key to survival
in wetlands,

where food is often hard to reach.

With their long legs,

black lechwe can wade
to the richest water meadows.

...and by flying, herons, egrets and storks
can find the best fishing grounds.

In the furthest reaches of Bengweulu

lives one of Africa's rarest
and most secretive birds...

...the shoebill stork.

It's a stealthy, sharp-eyed hunter...

able to spot the slightest stirrings
beneath the surface.

A lungfish.

Shoebills specialise in ambushing
large fish in small territories,

but most birds in the Benguelu swamp
need to search far and wide

to find the richest gatherings of insects,
frogs and fish fry.

By displaying and calling to one another,

groups of wattled cranes can
even communicate information

about the best feeding grounds.

Teamwork is also crucial for spoonbills.

Advancing like a Roman legion,
they drive small fish before them.

Swinging from side to side,

their bills create swirling eddies

which help them to sense
and scoop up the fish.

Ahead of them, black egrets
intercept the fleeing prey.

They're canny hunters...

using their wings
as umbrellas to create shade...

luring unsuspecting fish
right to their feet.

Rising and falling with the seasons,
the still,

shallow waters of Bengweulu have created
a simple - but magical wetland.

Far to the south of Bengweulu,

there's a very different type of wetland
...much more complex.

The Okavango in Botswana...

a river delta fanning out across the land
...never reaching the sea...

It's one vast tapestry of waterways.

Okavango is shaped by the land...
the water...

and sheer brute force.

Hippos are wetland bulldozers...

carving out channels that direct
the flow of water...

These waterways are always changing.

Vegetation and sediment close old routes...

...and flooding opens up new lakes.

In the central swamp
there is permanent water...

it's a mecca for hippos.

Here there's no fear of death
from drought.

Together this group represents 40 tonnes
of earth-moving equipment.

It's not just the hippo's power
which shapes the delta...

their dung also enriches the waterways...

which flush the valuable fertiliser
through the whole system.

The land here is almost flat and
the Okavango waters flow ever-so gently

...taking a full 6 months
to cross the delta.

Stands of fast-growing papyrus dominate
the upper reaches

where the water is a little faster...

Moving among these lazy waters are
fish like African pike...

seeking out new frontiers
to spawn and feed.

And tracking the movements of fish...

a range of hunters...
like the Bayei of Botswana...

...they net off channels to
intercept the migrating fish.

The clear calm waters of Okavango make
spotting prey from above easy...

...and African fish eagles are
sharp eyed hunters...

Eagles are spear fishermen...
but others here prefer to trawl.

Skimmers have a lower beak longer
than the upper,

allowing them to snap small fish
from the surface.

Nowhere else in Africa has such

a variety of different types of water
as Okavango...

the greatest inland delta in the world.

Seeing Okavango today,

it's hard to believe
that this region of Africa

was once a sun-baked desert.

It was only the chance movements
of the earth,

causing a river to alter its course
and spill across the land,

that created this waterlogged paradise.

And it's is not just a place
for swamp creatures...

...many savannah animals have also
found ways to exploit Okavango.

With their great powers of memory,

elephants quickly learn to
navigate the driest routes

between their feeding grounds.

It's not easy finding sure footing
in this boggy terrain...

The ever-changing flow of water is
always revealing new pastures,

so animals need to keep moving.

For lions, this means keeping up
with their prey...

which is no easy task.

Impala can take the water
in their stride...

...but for lions - like most cats
it's a real obstacle.

Buffalo are a potential target
for a large pride of lions.

...if only they could reach them...

There's only one thing for it...

Now the tables are turned.

The buffalo may have reached
their grassy island...

...but so have the hunters.

The waters now play to the lions advantage

...helping them to corral the herd.

These are crucial contests of
strength and cunning...

...but all life in Africa is at the mercy
of a far greater force...

...fresh water.

The water of Okavango has no
great lake to flow into,

nor does it ever reach the sea...

...all that life-giving water
going nowhere

...sucked away in the great emptiness of
the Kalahari desert.

Drought is the reality for much of Africa

...a continent so vast and so hot

that clouds can rarely penetrate
the interior.

But there is one other place in Africa

where wildlife can find water
in abundance.

In the central and northern reaches of
the Great Rift Valley

are a chain of weird and wonderful lakes

with names like Magadi, Nakuru,
Natron and Bogoria.

Though they look enticing...
these are no ordinary lakes.

Trapped in a world of volcanic turmoil,

their precious waters are contaminated
by sodium carbonate... the soda lakes.

Caustic and alkaline...

they are the fiercest waters in Africa...

More like a scene from another planet,

these bitter cauldrons are alien worlds.

But they are not lifeless.

One remarkable creature has found a way
to conquer them.

Flamingos, in their countless millions,
migrate up and down the Rift Valley.

They seem to instinctively know

when each lake has just the right balance
of water and soda to support them.

A riot of pink...

one of Africa's most dazzling spectacles.

With their long, thick-skinned legs,

flamingos can tolerate water so alkaline

it would scour the flesh off
other animals.

Though harsh, the soda-rich waters teem
with a unique form of blue-green algae,

which the flamingos siphon
through fine combs in their beaks...

By using the beak upside down,

flamingos avoid wetting their heads
in the bitter water...

it's a miracle of evolution.

Like all animals,
flamingos still need to drink

...but where can they possibly find
sweet fresh water in a place this?

Luckily for them,
around the margins of the lakes

there are clear-running springs,

bringing relief
from the depths of the earth.

It's also a chance to wash any soda off
their feathers and skin.

And every few years...

when the feeding conditions are perfect...

flamingos join together
in a magical courtship dance...

Africa's precious water dictates
the terms of life.

Even here in the harshest waters,
life can still triumph.

The waters of Africa's lakes and rivers

have shaped the evolution of
some remarkable animals...

...they unite its many worlds...

They are the life-blood of the continent...