(gentle music) [Narrator] Mangroves, swamps, and muddy floodplains may not sound all that inviting... but these rich habitats are extraordinary environments, literally bursting with life.

Wetlands cover just 5% of the Earth's surface, providing a haven for all manner of wildlife.

They're vital to human populations, too.

They act as natural water filters.

They protect our shorelines.

And reduce the impact of floods.

They supply us with an abundance of food... and contain a wide diversity of life that never ceases to amaze and surprise.

And with access to a boat and a good pair of wellies, we humans can get perhaps a little too close to a remarkable ark of animals.

During the wet season, most of northern Australia becomes a tropical, seasonal wetland.

These vast swamps support the world's largest breeding colony of magpie geese.

They also provide a habitat for the top end's top predator: the prehistoric saltwater crocodile.

If you think this well-armored warrior is big, just give him a few more decades to pump himself up and rise through the ranks.

By the time he's the boss croc around here, he'll be well over five meters long.

Saltwater crocodiles, or salties, as they are affectionately known in Australia, are the world's largest living reptiles.

The biggest in captivity today is over six meters and weighs just over a ton.

Saltwater crocodiles never actually stop growing and they can live for 70 years.

Once hunted for their skin and meat, they are now protected in Australia, and populations throughout the north are healthy, to say the least.

In the Northern Territory alone, there are estimated to be at least 100,000 salties lurking just beneath the surface, ever-ready to take down prey.

It's almost impossible not to fear these prehensile creatures... but they command, in equal measure, our respect.

Millions of years of evolution have fine-tuned them into the ultimate wetland predator.

The forward orientation of their eyes allows them to expertly judge the distance of unsuspecting prey.

And a third transparent eyelid means they can see as well underwater as above.

They can slow their heart rate down to a couple of beats per minute.

A very Zen-like skill that helps them to hold their breath underwater for up to an hour.

A saltie's jaws contain 64 to 68 dagger-like teeth... with a bite-force to rival that of a great white shark.

Their jaws contain an additional joint that helps to spread the full force of their powerful bites, so they don't lose their grip in the middle of an attack.

Crocodiles cannot chew, but will manipulate their prey to move it closer to the back of their throats before swallowing.

The safest way to encounter saltwater crocodiles is from a distance.

Wildlife guides are experienced in knowing exactly when it's appropriate to move in for a close-up and when it's better to slowly back away.

For a closer encounter still, consider swimming with these notorious man-eaters.

But make sure you're well protected by a cage, such as this, or you'll risk being eaten alive.

Salties are the largest reptilian predators on the planet, but even they lack the size and strength to take down this gargantuan beast.

Water buffaloes grow to 1.8 meters at the shoulder and have lethal horns up to two meters wide.

A young one would be fair game for a croc, but once they reach their adult size, they are pretty much invincible.

Water buffalo are not native to Australia.

They were introduced from Asia by settlers in the 1800s, who brought them here to ensure they had a reliable source of meat.

Then slowly but surely, they took over this seasonal wetland and the entire character of this landscape was altered.

They trampled vegetation, eroded the soils, created deep channels, and interfered with the quality of the water.

Their habit of wallowing muddied the water, making it difficult for certain aquatic plants and fish to survive.

As they degraded the habitat, they disrupted the nesting activity of magpie geese and crocodiles, so even these normally prolific species were compromised.

At the height of their domination, some 350,000 buffaloes roamed the nation's top end, but culling has now reduced their population considerably.

Here in Kakadu National Park, they number in the low hundreds.

It's ironic that these impressive animals need to be kept in check in Australia, for in their native homelands across Asia, they are a species at risk.

Without the protection afforded by nature reserves and national parks in India, Nepal, and Thailand, their survival in the wild would be completely compromised.

Wetland habitats throughout the world attract wading birds.

And with access to some form of boat or land-based hide, bird watchers can have a field day adding sightings of various species of herons and cranes to their endless checklists.

All wading birds have long, thin legs that help them to forage in deep water and long, agile toes that aid their balance when the ground beneath them is unstable.

Many wading birds have long bills shaped according to how they hunt and what they eat.

One special place tailor-made for waders is the Birds of Eden Sanctuary in South Africa.

A huge dome, covering several hectares, affords the birds here a measure of protection and yet the freedom to fly.

A walkway through the enclosure makes it easy to view some of Africa's most iconic wading birds... including these magnificent, and aptly named, spoonbills.

One of the more spectacular species visitors can encounter here is the scarlet ibis, whose native habitat is half a world away.

To see these beautiful birds in the wild, you'll need to head to Los Llanos in Venezuela.

A vast landscape of plains, rivers, and swamps stretching from the Andean Mountains to the Caribbean Sea, Los Llanos provides sanctuary to a strange collection of animals.

Primeval birds with claws on their wings.

Rodents the size of sheep.

And snakes the length of five people.

In total, Los Llanos covers over half a million square kilometers.

For more than half the year, these plains receive almost no rainfall at all and sizzle under drought conditions.

(thunder booming) But when the rains fall, they totally transform the landscape.

The grassy plains where the local cowboys, or Llaneros, hold court, rounding up their cattle on horseback, become inundated with water.

Los Llanos becomes a wetland wonderland.

It's Venezuela's greatest treasury of wildlife and its animals are some of nature's crown jewels.

Believe it or not, this capybara is a kind of guinea pig.

But it towers over every other rodent on the planet.

Despite their fearsome size, capybaras are gentle creatures, spending most of their time grazing or napping.

They're well adapted to living in water.

In fact, they even have webbed feet.

And their eyes, ears, and nostrils are all near the top of their heads, so they can hide their bulk underwater.

Apparently, capybara meat tastes delicious.

So much so, the Spanish colonialists who arrived here in the 1500s appealed to the Catholic Church to have the capybara classified as a fish so they could eat it on Fridays and other occasions when religious fasting needed to be observed.

Despite the fact that capybaras are quite clearly mammals, the church conceded to the argument that an animal with webbed feet, that lives mostly in the water, could be called a fish.

Another over-sized animal that frequents the swampy backwaters of Los Llanos is the giant green anaconda.

The largest snake in the world.

Just seeing one of these huge reptiles up close gets the adrenalin going.

So, spare a thought for these scientists, charged with extracting boas from the field in order to study them more closely.

Despite their intimidating looks, these snakes are not venomous.

They hunt by coiling themselves around prey and squeezing until it's asphyxiated.

The largest anaconda ever measured was just over eight and a half meters long, with a one-meter girth.

This one is considerably smaller, but still a handful for these scientists to contend with as they attempt to collect and record data that will help them to determine its growth rate and overall health.

The wetlands of Los Llanos are home to another giant reptile.

At nearly two meters long, green iguanas are among the largest lizards in South America.

The best iguana sightings are along the water's edge, where they venture to take in some sun.

In the trees, they can be quite well camouflaged, hiding out in the domain they share with the hoatzin.

This longtime resident of Los Llanos dates back to the time of the dinosaurs.

Another extraordinary place to encounter the best of South America's wetland animals is the Pantanal.

Indeed, it's the largest tropical wetland in the world... awash with lakes, waterfalls, and crystal-clear rivers.

Covering a daunting 181,000 square kilometers... it contains one of the highest concentrations of wildlife on the continent.

The jaguar's share of this UNESCO World Heritage Site is in Brazil and a key access point for exploring some of its amazing biodiversity is Bonito.

A short trek leads animal lovers through the jungle that lines the Rio Da Prata.

It's possible to encounter capybaras here... and if you're really lucky, armadillos and tapirs.

Despite their pig-like looks, tapirs are closely related to horses and rhinos.

Jaguars sit at the top of the food chain here and despite the fact that they are excellent swimmers, there's no need to fear an unexpected encounter here.

The water is so clear, you'd see them coming for miles.

What you will see below the surface of the water, however, will completely blow you away.

A swirl of orange-tipped fish.

The whole experience is quite surreal and it's heartening to know that a place this pristine still exists in the wild.

The Pantanal is truly a remarkable wetland, but it's far from the most well-known eco-region in this part of the world.

That honor belongs to the Amazon, South America's most iconic river.

Nearly six and a half thousand kilometers long, it snakes its way across seven countries.

The rainforests on either side of the Amazon hold a greater diversity of life than any other place on Earth.

20% of the world's oxygen is made by the plants of the Amazon and the number of different animals here is simply phenomenal.

Hundreds of mammals, thousands of birds and fish... and millions of creepy, crawly insects.

During the wet season, the Amazon floods and the width of the river expands.

In some places, it can be over 190 kilometers wide.

One of the most amazing creatures of the Amazon spends its life underwater and thanks to Hollywood's horror movie heavyweights, its reputation is unfairly tarnished.

Scientists dispute the whole Hollywood myth that a school of piranha can devour a person in a matter of seconds.

They believe it would take 300 to 500 of the tiny fish a good five minutes to consume a fully grown human.

So really, why all the fuss?

Lurking beneath the water hyacinths, growing to nearly three meters long, the manatee is one of the Amazon's largest animals.

Notoriously shy, even expert guides would count themselves lucky to see one.

Fortunately for animal lovers the world over, there's a rescue center in Peru where sightings of these curious creatures are 100% guaranteed.

The Amazonian manatee is one of only four manatee species in the world.

It's slightly slimmer than the other manatees and unlike its Caribbean and African cousins, has no nails on its flippers.

Sometimes called sea cows, manatees are gentle creatures.

They are herbivores that only eat two types of plant in the wild, water lettuce and hyacinth.

With each 300-plus kilo animal needing to consume 8% of its body weight every day, they sure put a dent in the salad bar.

To help them contend with all that chewing, manatees have quite unique teeth.

They are the only mammals that constantly replace their worn-out molars with new teeth that grow at the back of their jaw, moving forward when needed.

Manatees once lived throughout the Amazon Basin.

But thanks to high demand for their meat and oil, these lovely creatures are in serious decline.

But with careful human intervention, the Amazonian manatee population is slowly recovering.

North America's biggest wetland is a complete contrast to the Amazon.

It has very few trees and is dominated by one slow-flowing river, nearly 80 kilometers wide.

They call it the Everglades and it takes up most of the southern tip of Florida in the USA.

It's easy to see why this unique combination of shallow water and prairie is often called a river of grass.

It, too, is home to a manatee, the West Indian species, a larger relative of the Amazonian one.

It's not only possible to encounter Florida's manatees underwater, here in the King's Bay Wildlife Refuge, it's actively encouraged.

These gentle giants are mesmerizing to watch... curious and comfortable in the presence of humans.

There are more manatees here in the Crystal River during winter, as most migrate in the summer, travelling as far as Mexico or Massachusetts.

Not far from the city of New Orleans, on the southern coast of America, are the swamplands of Louisiana.

A wetland brimming with opportunities to encounter the state's top predator, the American alligator.

Alligators are not as big as saltwater crocodiles, but they're still a lot of primeval reptile to contend with, growing up to four meters long.

Needless to say, everyone in Louisiana treats them with a healthy respect.

Alligators are well-armed apex predators, with a preference for eating fish, snakes, and small mammals.

An opportunist, an adult 'gator will also go for carrion, the occasional pet dog, and sometimes, their two-legged masters.

By the mid-1900s, they had been hunted to the brink of extinction, but effective protection, coupled with habitat preservation and a reduced demand for alligator products, have allowed the species to recover.

The wild alligator population is now estimated to be over a million and growing.

One alligator that would struggle to survive in the wild is Claude, the albino.

He's gone from the Bayou to the big time.

According to his Facebook page, he's the main attraction at the California Academy of Sciences in San Francisco.

Direct sunlight would eventually kill poor Claude, so this facility has compensated by popping a heated rock into the middle of his enclosure to help him thermoregulate.

He is one of a dozen or so crocodilians in the world affected by albinism, a lack of melanin in his skin.

With no reason to be concerned about his distinct lack of camouflage here, Claude has become something of a swampland superstar.

On the other side of the world, East Africa is also a mecca for water-loving wildlife.

The Great Rift Valley, a series of cracks in the Earth, threatening in time to pull the continent apart, is best known as the place where mankind was thought to have evolved.

But we humans are just one species to have made a home for ourselves in this magnificent part of the world, awash with the wonder of wetlands.

Many of the Rift's great trenches now contain lakes, and these lakes are a haven for an astonishing concentration of wildlife.

Lake Naivasha in Kenya is one of the easiest to get to, a mere 100 kilometers from the capital Nairobi.

The animals you're most likely to encounter here are impressive to say the least.

This giant resident needs both water and grass to survive, so it's settled in well to Naivasha.

The hippopotamus can eat one and a half times its body weight in a single day.

And when you consider that a full grown male weighs around three and a half tons, that's clearly a lot of food.

The hippos around Lake Naivasha feast mainly on the papyrus grasses fringing the swamps.

They have to spend at least five hours a day eating just to survive.

But they generally do this at night.

By day, hippos tend to while away the hours cooling off in the water or resting in the shade, trying to keep out of the sun.

Hippos do not have sweat glands, so they can overheat quite quickly.

Their thick skin can crack if it's exposed to the air for too long.

Fortunately, however, they secrete a special oil to protect themselves from the sun's harmful rays.

Despite its alarming red color, it doesn't contain any blood.

It forms a kind of varnish that keeps the hippo's skin moist.

It also acts as an antibiotic and heals infections effectively.

A hippo's proportions are daunting, but it's hard to get past that remarkable jaw-dropping mouth.

Tusks in a male can get to 50 centimeters long and while they do wear down, they never actually stop growing.

Male hippos fight terrible battles when it comes to winning the right to mate.

Females will fiercely protect their young... and males are very territorial, so any encounter needs to be from a safe distance.

Hippos cause the most human fatalities of all the animals in Africa, so visitors to Lake Naivasha need to remain vigilant at all times.

Despite their land-loving ways, a hippo's closest living relatives are whales.

Their ears and nostrils close completely when they are submerged and they have a strange way of hearing underwater that's similar to that of a dolphin.

They use their lower jaws to pick up sounds, which are then transmitted to their ears via fatty tissue.

As wild habitats throughout the Great Rift Valley continue to diminish, hippo numbers continue to fall.

But for the time being at least, protection appears to be working for those lucky enough to have chosen Naivasha as their home.

Two hours' drive from Lake Naivasha is one of the most hostile wetlands on Earth.

Lake Nakuru.

The water here is so caustic it could burn human skin.

The soda lake contains so many salts and minerals it repels most of Africa's animals.

But one creature positively thrives here.

Over one and a half million flamingos live in and around Lake Nakuru.

They are perfectly adapted to survive conditions that would prove fatal to most.

Tough scaly skin on their legs prevents them from burning.

They have special glands in their heads to remove salt from the water when they're drinking, which then drains out through their nasal cavities.

They eat cyano bacteria, an organism that grows here in vast pink drifts.

It's a highly toxic creature that would destroy the liver and nervous systems of lesser animals, but the flamingo can eat it with gusto.

The only visible effect it seems to have on the flamingos is evident in their feathers.

All that pink algae is the cause of their scintillating color.

Flamingos feed by sweeping their bill upside down through the water.

Filters within catch the microscopic algae floating in the water and mud.

Flamingos can fly fast and travel far, up to 1500 kilometers.

So, one wonders why they would have chosen such a hostile niche for themselves in the first place.

Certainly, flamingos in other parts of the world have settled into less extreme places and adapted well to less challenging lifestyles.

But in adapting to this particularly toxic environment, Africa's flamingos find themselves with very little competition and a measure of protection from predators.

When hyenas, jackals, or eagles attempt an attack, all a flamingo need do is wade into the caustic water to stay safe.

Africa's most famous wetland lies in the middle of the desert and it floods just as the land around it begins to dry up.

This is the Okavango Delta... a massive body of water in northern Botswana.

The water that fills it each year comes from seasonal rains in the highlands of Angola, ultimately flooding 15,000 square kilometers of land.

Seeing this landscape and all the animals drawn to it, from the air, is an unforgettable experience.

The delta is a lifesaver for animals from far and wide.

A seasonal home to over 500 different bird species, 300 mammals and reptiles, and countless insects.

But the most impressive to see on the move are those that have come to this wetland oasis from the plains.

Great herds of zebra and impala, giraffes and elephants.

This is a dynamic environment.

Every year, the layout of the wetland is different, thanks to a range of pressures.

Sediment and vegetation block certain channels, while seismic activity and the movements of hippos open up completely new ones.

Eventually, the Okavango Delta peters out, with the water evaporating into the tropical air or sinking into the thirsty desert sands.

The Okavango is not the only wetland in Botswana where water-loving animals congregate.

This remarkable country has 17% of its land devoted to wildlife protection, but its very first national park was Chobe.

The land around the Chobe River in northeastern Botswana has been a haven for wildlife since 1968.

Decades of tireless conservation have allowed Chobe to build a veritable menagerie of wild animals... including the largest elephant population in Africa, 120,000 strong.

Getting close to these remarkable animals is a powerful, life-affirming experience, especially during the dry season, between April and October, when they tend to congregate along the Chobe River.

African elephants are the largest land animals on Earth.

A full-grown bull can be four meters tall at the shoulder and weigh six tons.

Bull elephants tend to lead semi-solitary lives, wandering alone or in loose-knit bachelor herds.

If you encounter a large herd of elephants, of all ages and sizes, they're probably all females and their young.

Female elephants will spend their entire lives in herds such as these, living as one big extended family.

Mothers, grandmothers, aunts, and sisters, plus an assortment of their offspring.

When a baby is born, every member of a herd will help to raise the young elephant.

Female elephants will only carry one calf at a time and since each pregnancy lasts for nearly two years, they will likely only calve four times in their lives.

Young calves are not fully independent until they are around 13 or 14 years old and reach their full size around 20.

Both males and females have tusks, a major tool in their quest for survival.

Each tusk is an overgrown incisor, but unlike human teeth, they never stop growing.

Another standout feature of African elephants is their trunks.

They contain 100,000 muscles and tendons and can stretch out to three meters.

The finger-like tip of the trunk can perform delicate tasks, like picking a berry or selecting a single juicy leaf.

These massive animals are herbivores so they have no interest in attacking humans unless they feel threatened.

Grass and leaves do not contain a huge amount of nutrition, so an elephant needs to eat over 100 kilos a day to stay alive.

They also need to drink up to 200 liters of water.

Despite their bulk, elephants are able to swim.

They can also walk on river bottoms, using their trunks as snorkels.

Those enormous ears also have a range of uses beyond hearing.

They are excellent cooling devices and an important means of communication.

Flapping ears are known to signify aggression or joy, depending on the circumstances.

Elephants have amazing hearing.

They can pick up sounds from 10 kilometers away.

With a brain three or four times bigger than a human, elephants are capable of intelligent communication, and are known to have exceptional memories.

They also show a complex range of emotions, expressing compassion, joy, and grief.

The elephant's capacity for sadness is well documented.

They are known to mourn the loss of a loved one in a very humanlike way.

Small wonder we find these huge animals so fascinating and endearing.

Australia's largest lake usually contains no water at all.

Most of the time, it's just a shimmering salt pan stretching as far as the eye can see.

When water does trickle into Lake Eyre, or Kati Thanda as it's known to the local aboriginal people, it comes from the rivers of Australia's central deserts.

It only rains sufficiently here to fill the lake occasionally, perhaps once every eight years.

Even when it buckets down, the water behaves somewhat erratically.

The channels feeding into the Kati Thanda Basin decrease their flow as they move downstream.

The flat nature of the land and the hot air that passes above it conspire to force the flow to either spread out or evaporate.

Any water that actually reaches the lake tends to be very salty.

The lake bed is the lowest point in Australia, 15 meters below sea level.

So, when rain falls, Kati Thanda is totally transformed.

Central Australia's vast floodplains turn into wetlands, brimming with life.

News travels fast in the natural world, especially when there's food around.

Birds normally found living by the seaside suddenly descend on Central Australia.

Pelicans arrive in their tens of thousands.

The Australian pelican has a wingspan of nearly three and a half meters.

And as you might expect, they're impressive travelers.

They can soar thousands of meters into the sky and stay airborne for 24 hours.

Between 30,000 and 50,000 pairs will arrive to take advantage of this instant inland bounty.

Many will have flown halfway across Australia, so there's no doubting they're hungry.

Pelicans can fit 13 liters of water in their bills, but here, they're more interested in fish, supplemented by the odd turtle or frog.

They are big birds, with big appetites, and once they're refueled, it's on to the important business of mating and nesting.

Incredibly, scientists now believe that pelican chicks communicate with their parents from inside the egg, indicating when they're too hot or too cold, which in this harsh landscape could be crucial to surviving incubation.

The chicks in their eggs have also been listening to the unique sound emitted by their parents.

When they emerge, they recognize them straight away, despite their uniform appearance.

Hatching happens after 35 days and both parents take care of their young.

The entire pelican community contributes to the wellbeing of the chicks, corralling them into boisterous creches.

Parents can leave to find food knowing their offspring are well taken care of.

Chicks need to grow fast.

They need to start their flying lessons when they're only three months old.

Kati Thanda will not remain a lake for long and when it dries out, the young pelicans must be ready to make the 1500-kilometer journey back to the coast.

Nestled in the southeast of Australia, the Great Otways National Park is a diamond of land wedged between the mountains and the sea, 200 kilometers west of Melbourne.

It provides a haven for some of Australia's strangest animals.

A carnivorous beast with a fierce nature and striking spots.

A spiky, ant-eating ball of weirdness with a tongue half as long as its body.

And this strange creature patrolling the main waterways.

A shy, secretive animal with venomous spurs on its heels, a bill like a duck, and a fur coat that's thicker than an otter's.

It owes its existence to the evolution of mammals and birds as they began to diverge 280 million years ago.

But of the many species of egg-laying mammals, or monotremes, that developed at that time, only two now remain in Australia-- the echidna and the platypus.

They use their bizarre bills to dig for food underwater, scooping up shellfish and worms, mud and gravel from the river bed.

They store everything in special cheek pouches until they return to the surface to eat.

Without the benefit of teeth, a platypus makes good use of the gravel it's collected to help grind the food it has found.

It is becoming increasingly difficult to encounter shy animals such as the platypus in the wild.

River otters are faring a little better in North America.

But the Asian small-clawed otter is now locally extinct in many areas of its range.

Fortuitously, these aquatic mammals breed well in captivity, where encounters are actively encouraged.

While zoos all over the world do their best to provide enriching visitor experiences... by far the most satisfying way to observe any wetland animal is in its natural habitat.

Living as nature intended... in some of the most remarkable places on Earth.

Lying between dry land and deep water, the profusion of plant life that continues to thrive where conservation is valued and protection has been assured will continue to support and shelter a watery ark of truly extraordinary animals.

(dramatic music)