Original subtitles

This is the least known of Africa's great rivers.

The Zambezi brings life to six countries

and its reach spans half a million square miles of southern Africa.

It's a river of thrilling spectacle

and wild surprises.

At times, the Zambezi's power can be almost overwhelming.

Yet it can be just as challenging when its waters all but disappear.

The fate of all life here is at the mercy of the ever-changing moods

of this great river.

In April, half a million tons of water

pours over the Victoria Falls every minute.

Just a few months later,

the Zambezi's most famous landmark has dried up.

By September, the drought is so intense

that for much of its course, the river has shrunk to almost nothing.

This leaves a great swathe of south-east Africa

deprived of its life-giving waters.

During the wet season,

the Zambezi flows for 1,600 miles

from its source in the Zambian Highlands

to the coast of Mozambique, where it empties into the Indian Ocean.

But by the end of the dry season, the river barely flows at all...

leaving the land at the mercy of a blistering sun.

The dwindling river draws in thirsty animals from near and far.

Its banks see a constant flow of traffic.

The desperate search for food

can keep elephants away from the river for days at a time...

..which must make their brief return visits all the sweeter.

Buffalo put in more regular appearances...

..dipping into the river morning and evening.

Hippos are even more tightly bound to the river.

As the Zambezi shrinks,

these dedicated bathers are forced to crowd together

into what pools remain.

HIPPO GRUNTS

They've spent the cooler night wandering the banks looking for food.

Daybreak sees them heading back to the river.

HIPPO GRUNTS

Hippos have thick, blubbery skin

and no sweat glands.

So overheating can be a real problem.

Wallowing through the heat of the day is one way

to help them keep their cool.

One hippo is late back from its nocturnal wanderings,

only to find its way to the river barred.

These hyenas are really pushing their luck,

picking on such an enormous victim.

But when times are tough, no opportunity can be overlooked.

HYENAS SCREAM

Hippos only feel safe in deep water.

But this late in the dry season,

that's a commodity in very short supply...

..forcing thousands to share the narrowing channels

that feed the Zambezi.

This stressful overcrowding leads to fighting

and the inevitable casualties.

The smell of death draws out the river's scavengers.

Within a few hours,

over 100 crocodiles have converged on the carcass from far and wide.

The younger ones hold back, while the larger crocodiles

squabble over the choice cuts.

Crocodiles are true survivors, able to go for months between meals.

So this one chance to feed will be enough

to get many through the hard times.

Others too are reaping the benefits of this overcrowding.

Wherever there are hippos, there are oxpeckers.

The hippos tolerate these birds because they remove ticks

and other skin parasites.

Their habit of picking at old wounds

to lap up fresh blood is much less friendly.

And hippos aren't the only choice open to these freeloaders.

Buffalo are plagued by their attentions, as they poke and probe,

feasting on bugs, dead skin, saliva...

even earwax.

Six months ago, these mud banks were completely underwater.

But as the river level has dropped,

carmine bee-eaters have moved in

to stake their claims.

Each nest hole must be dug anew each year,

after the Zambezi has reshaped its banks during the flood season.

Some colonies may contain several hundred pairs,

all crowded together for safety.

But the adults are still vulnerable to aerial attack.

An African fish eagle has taken up residence.

And it's developed a real taste for bee-eaters.

BIRDS CHIRP

Its feet are designed for grappling with slippery fish,

but they're just as good at snatching panicking birds.

It's another of the Zambezi's residents,

adaptable enough to make the most of any chance that presents itself.

By October, the river has pretty much reached rock bottom.

Out on the Zambezi's floodplain,

the intense heat is sucking the last water holes dry.

This warm, muddy water holds little oxygen for trapped catfish,

but asphyxiation is the least of their problems.

Marabou storks gather around the shrinking pool.

Smaller catfish can burrow into the mud to escape

and will even travel short distances over land to reach new pools.

But the larger ones have nowhere to hide.

In the heat, their fate is sealed.

Several hundred miles further inland,

and upstream from the Victoria Falls,

the situation around the Zambezi is just as desperate.

Along the river's banks, the land is turning into a dust bowl.

As the grass withers and dies, there's little left to eat.

Everything is hanging on,

hoping the river will soon revive their fortunes.

Wandering guinea fowl disturb a pack of hunting dogs.

The birds are of only passing interest.

These dogs are after bigger prey.

The pack exchange greetings as they steel themselves for the chase.

The dogs have been waiting for the cool of the evening...

but now it's time.

The pack is led by an alpha pair.

They decide when to move and what to hunt.

As they close in, the pack splits up, trying to outflank their prey.

Impala have speed.

But the dogs can run at 30 miles an hour...

..and have incredible stamina, as well as guile.

In their panic, the impala runs straight into the trap.

DOGS WHIMPER

Three quarters of all wild dog hunts end in a kill.

A group this size needs to kill every day.

And a river-side territory means they fare better than many.

Away from the river, the land is parched.

Life is a challenge for even the biggest

and smartest of the Zambezi's inhabitants.

With the river side vegetation exhausted,

hungry elephants have been forced away from the river

in search of food.

They can't afford to ignore anything.

Even a toppled tree gets the herd excited.

Little ones need to learn these twigs are edible

and some moisture can still be found in the bark.

But the adults need up to 200 kilos of forage every day...

..and lots of water to help digest such a high-fibre meal,

which means repeatedly trekking back and forth to the river.

Three or four days without a drink is just about their limit.

Local knowledge can make all the difference to survival.

It's intelligence the herd matriarchs have accumulated

over decades of wandering the plains.

Young calves begin to absorb this survival know-how

as they march at their mothers' side.

A fully grown elephant can easily drink 100 litres of water

in a single visit.

There's little time to linger,

although some seem reluctant to leave the comfort of the river.

But soon, this ordeal will be over.

The mood of the Zambezi is about to change.

The first signs of that change

can be seen above the rolling hill country of northern Zambia.

The Kaleni Hills rise just 1,500 metres above sea level,

but they are the green heart that will pump life back into the Zambezi.

Above these hills, powerful and opposing trade winds

begin to converge.

These collisions generate huge thunderclouds and torrential storms.

These first downpours mark the rebirth of the Zambezi.

From these hidden springs,

the great river begins to trickle its way to the sea.

As the streams combine,

the rejuvenated Zambezi begins to gather strength

as it curves westward into Angola.

These forest glades are the last stronghold of giant sable antelopes.

The darker males carry huge, curved horns

that can grow to over a metre and a half.

For 30 years, there were no sightings of these animals.

Then, in 2005,

this one herd was rediscovered.

With only a few hundred left,

every new addition helps bolster the sables' dwindling numbers.

For the moment at least, these highly-endangered antelopes

have found a sanctuary on the banks of the Zambezi.

As the river swings back east and re-enters Zambia,

it leaves the sable and the forests far behind.

The growing Zambezi begins to wind its way across the Barotse Plains.

These first rainstorms have partially refilled

some of the long-dry water holes.

After months on the move,

the pressure on the great herds of buffalo finally eases.

As the plains turn from brown to green,

the buffalo can settle down to the serious business of eating,

spending up to 18 hours every day grazing the new grass.

The Losi people have lived alongside the Zambezi for generations,

adapting to it many moods.

Before the water levels begin to rise, there's time to visit

a favourite fishing hole to plunder the last of the trapped catfish.

Soon, this grassland will be unrecognisable

and the Losi will be forced to move on to pastures new.

They will not be the only ones on the move.

As the rains gather in strength,

others are being drawn towards the Zambezi.

Small groups of blue wildebeest begin to arrive,

after a 200-mile journey south from the forests of Angola.

30,000 will eventually gather here.

It's one of the largest, yet least known migrations in Africa.

They are here to graze the fresh grass...

and to calve.

Almost all wildebeest calves are born within a three-week period,

flooding the Zambezi's plains with new life.

But they have already attracted some unwelcome attention.

A clan of hyenas begin to shadow the growing herds.

Their hunting strategy is simple...

Get the herd moving.

Look for a weakness...

..then strike.

The hyenas move in amidst the chaos, searching for a victim.

The calf makes it back to the safety of the herd.

Its mother is not so lucky.

The clan soon gather around the downed wildebeest.

Despite having so much choice, nothing is wasted.

All too soon, the wildebeest will move on.

And the hyenas' time of plenty will disappear.

By January, the storms are coming thick and fast.

The river channel can barely contain the torrent.

After months with so little water,

the Barotse's residents are about to be confronted

by a very different Zambezi.

The flood surges out over the river banks,

inundating thousands of square miles.

Almost overnight,

the grassy plains are transformed into a shallow inland sea.

More migrants arrive, following the advancing flood...

..their growing numbers adding

to one of the greatest gatherings of birds anywhere on the planet.

The rising water has suddenly got everything on the move.

Insects, frogs and fish all make their way

onto the flooded plains to breed.

Easy pickings for the hordes of water birds.

Even ground hornbills take advantage,

stalking the shallows.

Spoonbills sift the grasses for snails and minnows,

while yellow-billed storks tackle bigger fish.

But while these new arrivals make merry,

others are now forced to move on as the waters deepen.

The buffalo herds bulldoze their way towards higher ground.

The blue wildebeest continue their wanderings.

It will take five months for them to complete their return journey

back to the Angolan hills.

Lechwe antelope are in their element.

Strong swimmers, they never stray far from water.

But even they must move to keep pace with the rising tide.

The relentless Zambezi forces both predator and prey into full retreat.

April marks high water on this stretch of the Zambezi.

The river's floodplain is now 20 miles wide.

It takes weeks for the floods to cross these flat expanses,

as if the river is drawing breath before plunging on toward the sea.

The Losi too have learnt to adjust to the rhythms of the great river.

Their villages first become waterlogged...

..then, gradually, submerged.

Soon, they will abandon their huts, driven out by the rising tide.

But they can't just up sticks and leave.

By tradition, they must first wait for the signal from their king.

Today has been decreed as the moving day - the Kuomboka.

The word means literally "to get out of the water."

CHEERING

It marks the time when the entire community moves to higher ground

and in some style.

An elephant decorates the King's barge.

A crane perches on the roof of the Queen's.

100 men peddle each of the royal barges across the flooded grasslands.

It takes hours in the boiling heat

and humidity to reach their summer villages on the edge of the plains.

The Losi may be away for six months or more,

but it's a disturbance well worth putting up with.

The silt left behind after the floodwaters recede

invigorates the plains, preparing it for the returning villagers

to plant their crops and graze their animals.

The Kuomboka is a celebration of the gifts the Zambezi brings

to this part of Africa

and of how much the rise and fall of the river dictates life here.

For now, the Losi villages stand empty, deserted by the people

and their livestock.

But there is life here still.

New lodgers flood into the abandoned settlements.

Carp, minnows and cichlids pick over the remnants of village courtyards.

The flooded houses make perfect breeding grounds

for many Zambezi fish.

Others use them as shelter from predatory tigerfish.

But stray too far from cover

and there are other hunters waiting to drop in.

Able to hover and eat on the wing,

pied kingfishers are perfectly at home

fishing over the flooded grasslands.

As the floodwater finally reaches the southern end

of the Barotse plain,

it is gently funnelled back into the main channel of the Zambezi.

Now, over 700 miles from its source,

the great river gathers itself for the next stage of its journey.

Heading east again, the Zambezi begins cutting through

the tough volcanic rocks of the Tonga Plateau.

Ahead, a cloud rises half a mile into the sky.

It's not smoke from a bushfire,

but spray.

Visible from 20 miles away,

this cloud signals the most famous landmark on the Zambezi.

This is Mosi-oa-Tunya -

the smoke that thunders.

To the wider world, these are the Victoria Falls.

In full flood, this is the largest sheet of falling water in the world.

Over half a million cubic metres of water pour over the lip every minute.

At this time of year, the falls are over a mile wide.

And the cascade throws up enough spray to sustain

a unique rainforest along the Zambezi's banks.

Once the surge has passed, the local fishermen move in to try

their luck, in what must be the most exclusive fishing holes in the world.

Generations have made the precarious journey out to this pool.

One false move and it's a drop of over 100 metres onto the rocks below.

The Victoria Falls are a pivotal point on the river.

From here, the Zambezi leaves the wild plains far behind

and powers on towards a new and very different world.

Below the falls, the river cuts through

the first of several deep gorges.

The Zambezi is squeezed into a channel just 100 metres wide.

The power of the compressed river is immense.

Over millions of years,

this slow attrition has carved a series of steep-sided canyons.

Deep and inaccessible, these gorges have been cut a centimetre at a time

by the raw energy of the river in full flood.

For over 100 miles, the Zambezi zigzags its way east,

driving on towards the coast.

But as the river bursts from the last of these canyons,

the current slackens

and the flood lost in the deep waters of Lake Kariba.

Over 180 miles long, this is one of the largest lakes in Africa.

But only 60 years ago,

these islands were hilltops, because this lake is a recent addition

to the Zambezi's ancient course.

Holding back all this water is the Kariba Dam.

It was the first of several huge dams which now help control

the flow of the Zambezi...

..converting the elemental energy of the river into electricity

for Zambia, Zimbabwe and South Africa.

After the dam was completed in 1959,

it took just four years for Lake Kariba to fill.

As the waters backed up behind the new dam,

a massive rescue mission known as Operation Noah

was mounted to help animals caught out by the rising tide.

A group of dedicated wildlife rangers

moved in to deal with the stranded animals

ELEPHANT TRUMPETS

Larger animals were sedated...

..then moved to newly-established national parks along the lake shore.

Small animals were stampeded into nets.

DEER WHINE

It was a dangerous business for all involved.

It was the first time such an ambitious wildlife rescue

had ever been attempted,

but Operation Noah was hailed as a triumph.

Over five years,

more than 6,000 animals were removed to safe ground.

RHINO GRUNTS

RHINO ROARS

Although clearly some were less than grateful for the efforts

made on their behalf.

RHINO ROARS

While the rescued animals lived to fight another day,

the dam itself changed the Zambezi's character forever.

Robbing the river of much of its essential wildness.

Today, the seasonal floods on the lower reaches of the river

are no longer dictated by nature,

but largely controlled by engineers.

Yet enough water is still released from the dam

to keep the river flowing

and every rainy season, the Zambezi spills out of its main channel

and floods into a series of ancient lakes and stream beds.

These are known as the Mana Pools.

ELEPHANT GRUNTS

The barren earth bursts into life with grasses

and seeds that have lain dormant for months.

This flush of green draws in game animals

all along the fringes of the river.

Young hippos hide away in the quieter backwaters.

Many of these pools are now choked with water hyacinth, a fast-growing,

invasive weed, introduced from the Amazon in the 19th century.

But these floating mats block out the light

and starve the water of oxygen, choking all other life.

Although hippos and elephants seem to adore it.

So the more they can eat, the better it is for the health of the pools,

but they have quite a job on their hands.

The flooding draws even reluctant bathers into the water.

INSECTS BUZZ

Baboons certainly don't enjoy getting wet,

but the chance to feast on snails and flowers proves irresistible.

Along the tree-lined banks, other Zambezi residents

seem much more at home.

Fish eagles don't miss a trick.

With the bee-eaters long gone, they have turned their attentions

to the shoals of fish that gather in the shallows.

They can even turn the tables

on the tigerfish, one of the most voracious of the Zambezi's predators.

BIRDS SQUAWK

For a brief moment, the flooded pools are a magnet for many

along the stretch of the Zambezi.

Smart hunters stake out the water holes.

Waiting and watching.

These buffalo are nervous.

They sense something is not right.

They hightail it for cover.

When threatened, buffalo bunch in a defensive group,

with the calves gathered together and larger adults running shotgun.

The lion is persistent, but when he catches up,

one of the herd's enforcers proves more than a match.

The rest of the herd move in as back-up.

Buffalo are notoriously bad-tempered

and quite capable of dispatching a lion.

But today, it's only his pride that's been injured.

After months of rain, the Zambezi is about to change moods once again.

Storm clouds still build over the river each afternoon,

but these last downpours have lost much of their power.

The rain does little but kick up the dust.

ELEPHANT GRUNTS

All along the Zambezi,

animals once again start preparing for harder times.

But on one of the river terraces, a rare treat.

An ancient fig tree has burst into fruit.

A Trumpeter Hornbill shares the figs with a troupe of baboons.

Fig trees can crop at any time of the year

and these fruits always attract a crowd.

As the heat intensifies, acacias begin shedding their seed pods.

These are irresistible to bull elephants.

In a good year, one tree may produce 300 kilos of seeds.

For the tree, it's a great way to spread its seeds.

For the elephants, these are rare and welcome morsels,

packed full of energy.

It's a chance for everyone to stock up.

There are no giraffes here, so every extra centimetre gained

gives these bulls exclusive access to more food.

But it can be a precarious balancing act.

Some elephants go to extraordinary lengths to reach the best leaves.

ELEPHANT ROARS

Bulls can weigh over 5,000 kilos

and these acrobatics must place immense stresses

on their spine and legs.

But it's worth the risks to gather in the last of the greenery.

Soon, life all along the Zambezi

will become much more challenging, as the dry season begins to bite.

Beyond the Mana Pools, the river continues eastwards

through an ancient rift valley, heading towards Mozambique.

The Indian Ocean is only a few hundred miles distant.

But already the water level in the river is dropping.

HIPPO GROANS

Once again, hippos begin crowding

into the deeper stretches of the Zambezi and its tributaries.

Adults tend to hog the deeper parts of the river

and the youngsters have learnt to give them a wide berth.

They form their own gangs on the fringes,

where their curiosity can get them into all sorts of scrapes.

In the main channel, a dominant bull controls each stretch of deep water.

He will tolerate others,

as long as they behave themselves and defer to him.

This muck flinging is all about intimidation.

Crowded together, cheek by jowl,

it's only a matter of time before tensions erupt.

The shockwaves ripple down the line.

Once the pecking order is restored, everyone settles down,

but there's unfinished business here.

Fights can last for hours and if opponents are well matched,

can be to the death.

The dominant male has reasserted his right to be the leader

and so monopolise the females along this stretch of river.

For a while longer, elephants can still take things easy.

ELEPHANTS RUMBLE

The bank-side vegetation is not yet exhausted,

so they can stay close to the river.

There's even the odd moment for them to indulge themselves.

River mud makes an excellent screen against the blistering African sun.

This very young calf is none too steady on its feet...

..and soon needs rescuing by its ever-attentive mother.

Elephants are great swimmers.

River crossings hold few fears.

Their snorkels allow them to continue

even when fully submerged.

There's time to spend a few minutes enjoying each other's company

and the cool of the water.

Soon, life will become much more serious.

As food becomes harder to find, the elephants will again

be forced to spend more and more time away from the river.

As times get tougher, the Zambezi will once again become

the vital lifeline on which all can depend.

After 1,600 miles,

the Zambezi is nearing the end of its epic journey across southern Africa.

Here, on the flatlands of Mozambique,

the great river mellows as it begins to divide into a maze

of smaller channels.

As the flow eases, silt carried from the heart of Africa

begins to settle

creating a huge delta that reaches out into the Indian Ocean.

Today, this delta covers over 4,000 square miles,

but just 60 years ago, it was twice this size.

This dramatic decline is due mainly to the huge amounts of water

being held back by the many dams upstream.

Yet the river still empties vast quantities of fresh water

into the Indian Ocean.

But even as this mixes with the salt water, its journey is not over.

Already, the heat of the sun is sucking droplets

back up into the sky.

These clouds are carried far inland by the trade winds,

where they release their precious cargo as rain.

Rain that replenishes the flow of the Zambezi,

and so continues the endless recycling of water

that is so crucial to life.

Despite our best efforts to tame its many moods,

the Zambezi remains one of Africa's greatest and wildest rivers.

Subtitles by Red Bee Media Ltd