♪♪ NARRATOR: Hidden in the heart of Africa lies a place of wonder.

♪♪ This bountiful terrain draws migrants in their thousands.

But not all can make such journeys, and so this rugged land is the permanent home of three tribes.

[ Hippos grunting ] Hippos... crocodiles... ...and lions.

Each wary of the other... [ Crocodile hisses ] ...their stories unfold in parallel.

[ Thunder rumbles ] They live in harmony -- more or less -- until a fierce climatic cycle turns their world upside down.

♪♪ Relentless drought turn tussles over territory... [ Elephant grunting ] ...into battles for survival.

[ Thunder crashes ] What should be life-giving rain delivers floods of biblical proportion.

These age-old floodplains are no longer ruled by vagabond lions... [ Lion growls ] ...but by a greater power.

This is Katavi.

♪♪ ♪♪ NARRATOR: At the heart of Africa's Great Rift Valley in western Tanzania lies an ancient ribbon of land, remote and inaccessible.

Katavi is almost 2,000 square miles of unspoiled wilderness.

♪♪ But now the plains are parched beyond recognition.

In this unforgiving land, a rogue lion seeks to infiltrate the resident pride and sire his own young.

To escape his violence, the pride's oldest female, Patch, keeps her family on the move.

But the rogue is on their trail.

♪♪ Patch is ever vigilant.

The rogue has already killed two of the pride's cubs.

♪♪ To secure his own bloodline, he will need to kill them all.

♪♪ He will wait and choose his moment.

♪♪ [ Lion grunting ] ♪♪ But the rogue has competition.

[ Lion grunting ] Arthur, the pride male, has returned to Katavi.

[ Grunting continues ] He calls for his family, but it's the rogue who is listening.

[ Grunting continues ] ♪♪ [ Lion mewls ] These are roars of a strong and powerful lion, a lion in his prime.

[ Lion mewling ] A lion who will fight to defend his pride and his progeny.

The rogue must decide if this is a lion he's willing to challenge.

♪♪ Katavi is drier than it's been in a hundred years.

It's seen no rain for six months.

Clouds gather but hold on to their cargo of moisture.

Every animal here is feeling the heat.

♪♪ Finding food and water is getting harder by the day.

♪♪ The river's dry banks are devoid of prey.

♪♪ [ Crocodile growls ] A leopard is no match for a crocodile, and she's smart enough to move on quickly.

♪♪ [ Elephants trumpeting ] The river has dwindled to just a few brackish pools where animals are forced to congregate.

Hippos don't like being in such close proximity to lions... [ Hippos grunting ] ...but there's nowhere else to go.

♪♪ The lions have no choice but to drink, though the water is putrid.

♪♪ ♪♪ Curiosity and hunger draw a young male to the riverbank cave.

Only crocodiles, some of which live for a hundred years, have experienced a drought of this intensity before.

[ Lioness growls ] It will take more than an upstart cat to get her out of her sanctuary.

[ Lioness growls ] ♪♪ Elephants and lions have never been allies.

[ Elephant grumbles ] ♪♪ But today, the elephants are unusually eager to drive the lions away from the water.

[ Elephants grumbling ] ♪♪ Only when the rest of the herd arrives does the reason become clear.

[ Elephants grumbling ] Their youngest member is badly hurt.

Elephants are emotionally very similar to humans, and the herd care for this little one as we would an injured child.

A mud bath is a family affair, helping to strengthen their bonds.

♪♪ ♪♪ Now the lions have been put in their place, the herd can relax a little and enjoy a wallow.

♪♪ ♪♪ A coating of mud will protect their delicate skins from the relentless sun.

♪♪ ♪♪ ♪♪ It's a tantalizing spectacle for the lions.

♪♪ An injured calf is the perfect target.

But this youngster's bodyguard is mighty.

The lions must look for a less well-guarded prey.

And in such straightened times, Patch is always on the lookout for an opportunity.

Warthogs are small and usually not worth the effort of a hunt.

But the pride is hungry.

Patch has a strategy.

She slips off the riverbank, keeping low and out of sight, creeping closer to her quarry.

♪♪ The pride is on alert.

Patch's cover is blown, but it's all part of her plan.

She's surreptitiously herding the warthogs towards the pride.

Her daughter Mwezi understands the assignment and loops round to cut off the warthogs' escape.

♪♪ ♪♪ Mwezi has locked on to a target.

♪♪ Her paw pads on the bone-dry sand are silent.

♪♪ [ Warthog squeals ] The warthogs have been keeping an eye on the wrong lion.

♪♪ [ Lionesses growl, warthog squeals ] A mistake that costs one of them its life.

The hunt puts everyone at the mud hole on edge.

The pride makes short work of their small kill.

Before Patch even gets a mouthful.

[ Elephant grumbling ] ♪♪ The river hasn't flowed for weeks.

The hippos are crammed into the few remaining ponds in the deepest meanders.

In such close contact, hippos can be highly aggressive.

It's a dangerous place for a baby.

♪♪ There are threats on all sides.

♪♪ This protective mother is taking no chances.

And puts even a small croc in its place.

♪♪ [ Hippo bellows ] ♪♪ It's unheard of for crocodiles and hippos to mingle so closely.

But extreme drought is forcing everything here to behave abnormally.

Katavi gets more hellish every day.

For a mother and baby, the situation is particularly dire.

♪♪ Hippos cannot sweat to keep cool.

Without refuge in water, the baby runs the risk of overheating.

She desperately tries to stay in the shade of her mother.

But she's growing weaker.

♪♪ ♪♪ Displacing crocs is risky, but they must cool off.

♪♪ And at last, a few inches to lie in.

[ Hippos grunting ] But their next-door neighbor doesn't want to share, and it's the final straw for this overwrought mother.

But losing her temper causes a ripple effect and the whole pod erupts into chaos, which could put her baby in more danger.

A huge croc has become trapped in the middle of the hippo soup.

His only escape is to crowd surf.

It's a stunt that could cost him his life.

A hippo's jaws are powerful enough to bite a crocodile in half.

♪♪ But he must take his chances and run the gauntlet.

♪♪ ♪♪ The baby hippo has survived the rampage and found deeper water at last.

[ Hippos grunting ] And the croc makes it safely to the bank.

But his problems are far from over.

Arthur is searching for his pride.

This river bend is one of their old haunts, but it is almost unrecognizable.

[ Hippo bellows ] Even in the dry season, this is usually a peaceful stretch of river with plentiful opportunities for quenching thirst and ambushing prey.

Those days are a distant memory.

Now it's an overpopulated, fetid puddle.

♪♪ Some of the crocodiles are behaving strangely.

♪♪ Several of the oldest, their ancient bodies stressed by the extreme drought, are succumbing to a deadly virus.

♪♪ The specter of death hangs heavy in the air.

♪♪ Once formidable giants are wracked by uncontrollable convulsions.

♪♪ ♪♪ Until, with a last gasp of air, their suffering is over.

None have witnessed such a happening before.

♪♪ Katavi is in the grip of a dreadful higher power.

As more crocodiles are stricken, distress creeps through the whole community.

How many more will fall victim to this terrible fate?

♪♪ Arthur's quest to reunite with his family seems more urgent than ever.

Distant thunder is a torment.

[ Thunder crashes ] On the far horizon, taunting rain.

But then... a miracle.

♪♪ ♪♪ Katavi's lifeblood is awakened.

[ Thunder rumbles ] ♪♪ Its faraway headwaters replenished by the storm.

The river is reborn.

♪♪ Water that has been stagnant for weeks begins to shift and swirl.

♪♪ Inch by inch, the river advances, carrying with it the promise of salvation.

[ Thunder rumbles ] ♪♪ Cracks fill, bend by bend, from far and wide.

♪♪ The current strengthens.

Despair gives way to hope.

Those who have been imprisoned by the drought dare to believe they will be set free.

Water keeps on coming.

The river unfurls and spreads through Katavi's broken landscape.

♪♪ ♪♪ [ Thunder rumbles ] ♪♪ ♪♪ Reaching every wretched bend.

♪♪ Following the river, the storm races in, and at long last, rain returns.

♪♪ Slowly, the shackles of drought are loosened.

[ Thunder crashes ] ♪♪ The hippos and crocodiles tentatively adjust to their new reality.

♪♪ They are liberated.

♪♪ ♪♪ Relief has come too late for some.

♪♪ But for many, this deliverance is just in time.

♪♪ Only the water has the power to draw the old matriarch from her cave.

[ Thunder rumbles ] This is change she always knew would come, as it did in the previous century.

The rain persists.

The river continues to rise, bringing release to those previously trapped in isolation by mud turned to clay.

Gradually, the realization dawns that they are free to search out and reconnect with their own tribe.

[ Thunder rumbles ] The worst is over.

At 3 months old, this lucky one percent of surviving hatchlings now has a greater chance to reach adulthood.

The mother hippo can move her baby to a different place.

Away from the crocodiles.

Away from the crowds.

Away from danger.

At last, Katavi's river tribes can relax.

And rejoice in the rain.

[ Hippos grunting ] [ Thunder rumbles ] Everyone has space to spread out.

Tension washes away, and Katavi's giants remember their gentler sides.

For Arthur, the torrential rain presents a problem.

He won't be able to find his pride in the storm.

[ Thunder crashes ] It keeps on raining.

For the lions, the change in weather should herald the return of prey.

[ Thunder crashes ] But once again, Katavi is experiencing an extreme.

[ Thunder rumbles ] Rain like this hasn't been witnessed in a hundred years.

A few days ago, the pride was at risk of dehydration and heat exhaustion.

Now there's no escape from the wet and the cold.

[ Thunder crashes ] Day and night, the storm keeps raging.

[ Thunder crashes ] ♪♪ Filling every tributary and stream.

♪♪ ♪♪ Bursting the river's banks.

♪♪ ♪♪ ♪♪ And delivering floods of biblical proportion.

Katavi is transformed into a vast wetland.

So unlike the hostile dry landscape of the drought, it's hard to believe it is the same place.

♪♪ ♪♪ This new Katavi is a paradise for hippos.

♪♪ And crocodiles.

♪♪ A magnet for waterfowl.

♪♪ ♪♪ But for some, survival in this water world could be impossible.

The swollen river has formed islands separated from the mainland by deep channels.

The lion mothers have become separated.

Mwezi and her cubs are safe.

But Patch and her young are stranded on an island.

The only way off is to swim.

A daunting prospect.

In the fast-flowing water, a lion cub could easily be swept away.

[ Elephant trumpets ] The elephants demonstrate the dangers.

♪♪ Using their trunks, the adults sweep for crocodiles.

Elephants are strong swimmers and naturally buoyant.

Even so, the youngest is out of his depth and needs to use his trunk as a snorkel.

[ Elephant calf trumpets ] ♪♪ ♪♪ ♪♪ The herd is safely across.

But the lion family would do well to wait and hope the waters recede.

Deep water is an almost forgotten delight for hippos.

But they don't just enjoy it, it's essential for their survival.

Surrounded by water, the mother and her calf can at last travel safely, confident they will find a place to call home.

♪♪ With an abundance of river real estate, hippo society is returning to normal.

♪♪ Young males spar amicably, just as they should.

♪♪ For grazers, this flourishing new world is the Garden of Eden.

♪♪ But Patch knows her cubs are in trouble.

Still reliant on her milk, they won't survive long if she can't keep up the supply.

She needs to hunt.

And that means leaving them alone on the island.

Patch treads carefully.

The river holds more dangers than just deep water and strong currents.

[ Thunder rumbles ] Safely across, now the night's work begins.

[ Thunder crashes ] The rumble of an imminent storm works in Patch's favor for once, muffling her footsteps and making it easier to sneak up on her prey.

[ Thunder crashes ] Her night vision is six times better than ours.

But the zebra's stripes make them very hard to pinpoint.

[ Zebra braying ] She's charged too soon.

[ Thunder crashes ] The zebra slips.

[ Zebra brays ] [ Braying continues ] [ Braying continues ] Patch wins her prize.

[ Thunder crashes ] [ Zebra brays weakly ] She'll spend the rest of the night enjoying her well-earned feast.

♪♪ ♪♪ A fresh new dawn.

[ Birds chattering ] And once again, birds can move freely to exploit the emergence of a multitude of diverse prey.

♪♪ ♪♪ By morning, belly full, Patch is ready to return to her cubs.

♪♪ ♪♪ [ Hippos grunting ] But someone else is heading their way, too.

[ Lion roaring ] Arthur.

[ Roaring continues ] With no shortage of water, he's been able to widen his search for the pride.

His cubs were born after he left, unbeknownst to him.

He's almost caught up with his own young.

[ Lion roars ] His roars carry through the still air, a sound that makes the cubs very nervous.

The last time they met a big male lion, he killed two of their siblings.

♪♪ They've never met Arthur and don't know that he's their father.

♪♪ Arthur has picked up their scent.

♪♪ He's getting closer.

♪♪ Frightened, the cubs instinctively move away from the approaching sound.

Scuffing signals Arthur's intention to stake his claim.

♪♪ [ Cubs mewling ] ♪♪ Crossing even a small channel is a big step for the little cubs.

♪♪ ♪♪ But the splashes are drawing unwanted attention.

♪♪ ♪♪ Arthur is getting nearer.

♪♪ And now they've reached a dead end.

He's closing in.

♪♪ Trapped on the peninsula, the cubs are at a loss.

But then, a familiar sound... [ Lioness mewls ] ...from the opposite bank.

Patch is calling to them, letting them know she's on her way home.

[ Lioness mewls ] Arthur's long search is finally over.

The cubs are not where she left them the night before.

They are torn between facing a stranger and the dangers of crossing.

Patch has no idea of the risk they're about to take.

♪♪ The bravest takes the plunge.

He's out of his depth immediately and the current is strong.

♪♪ But instinct keeps him paddling.

♪♪ His brother is hot on his heels.

They need to be quick.

♪♪ Two safe.

And the third.

Arthur's chosen quite the moment to see his cubs for the first time.

His arrival, a big surprise for Patch.

[ Lioness mewls ] Against the odds, all three cubs have survived their daring crossing, and they're very glad to be reunited with their mom.

Arthur wisely bides his time.

The cubs have had enough excitement for now.

♪♪ At long last, the buffalo mega herds return to Katavi.

And with plenty of water and new grass growth, they're likely to stay.

♪♪ This is just the change in fortune Patch needs.

The presence of big animals like buffalo encourages lion prides to stick together and maintain family ties.

Because hunting buffalo is not something Patch can do alone.

♪♪ Cubs safely stashed, the pride assembles on the edge of the plains.

The zebra needn't worry today.

Patch has got a different objective.

[ Hippos grunting ] The lions move into position.

Gone is the tension of recent weeks.

Their demeanor is relaxed and confident.

These are buffalo hunters, a crack team, preparing to do what they do best.

[ Thunder rumbles ] Normality is returning to Katavi.

An old termite mound provides just the rise they need to watch the herd.

They have gathered here many times before to assess their prey.

[ Buffalo lowing ] This feels like old times, good times.

No need to rush.

Desperation can cause mistakes.

But now they're calm and in complete control.

♪♪ Arthur's timing couldn't be better.

♪♪ Together, the pride is united and strong.

♪♪ ♪♪ The herd is inching closer to the forest where the cubs are hiding.

They'll have ringside seats to observe the action.

♪♪ The fading light can only be to the lion's advantage.

Buffalo are dangerous.

The trick is to single out the right quarry.

[ Buffalo grunts ] A straggler.

♪♪ ♪♪ The lions carefully slip into position.

♪♪ ♪♪ In a pincer maneuver, they sneak up on both sides.

[ Buffalo lowing ] A buffalo hunt is a family affair.

[ Lionesses growl ] [ Lioness mewls ] Patch calls the little ones in.

♪♪ They need to learn what it takes to kill a beast like this.

Lionesses are supreme strategists, but Arthur's extra muscle brings the buffalo down.

[ Buffalo grunting ] ♪♪ This is the cub's heritage.

Arthur and Patch reinforce family bonds through this age-old hunting ritual... ♪♪ ...passing it on to the next generation.

♪♪ ♪♪ The ancient natural cycle of Katavi is restored.

♪♪ Life here has survived a climatic upheaval witnessed only once in a century.

♪♪ The harshest drought in living memory has broken, and the biblical inundation that followed has subsided.

♪♪ ♪♪ Once again, the rhythm of life swells and ebbs with the seasons.

♪♪ A new generation of lions is born.

Arthur patrols their territory but his wandering days are behind him.

Making life easier for Patch.

And Mwezi.

♪♪ Growing up with their father, these youngsters have the best possible start in life.

Protected by a powerful pride male.

♪♪ And the remoteness of one of Africa's last great wildernesses.

♪♪ Hippos have plenty of deep water.

And they squabble over status rather than fighting for their lives.

But as our planet heats, devastating climate anomalies could become more frequent.

Katavi's dry seasons could become far harder to endure.

♪♪ And the apocalyptic conditions once separated by many decades could become part of every young lion's future.

But for now, they survive.

One hunt at a time.

♪♪ ♪♪ ♪♪ ♪♪ ♪♪ ♪♪ To learn more about what you've seen on this "Nature" program, visit pbs.org.

♪♪