[Narrator] Every wild corner on our magnificent planet harbors a great diversity of life.

From the huge schools of fish that fin their way through our seas to the great herds that thunder across land, the entire web of life that endures on earth owes its existence to water.

Most of the water on our planet is salty or locked up in glacial ice.

But the rest flows freely as rivers, beautiful and powerful waterways that underscore the melody of life.

♪ As freshwater drains off the land, it flows into a network of streams that braid together to form rivers.

As they meander through the landscape, they shape it, wearing down ranges and deepening valleys.

Most get broader as they get bigger, eventually forming estuaries or deltas where they flow out into the sea.

And in terms of volume, the world's largest river is the legendary Amazon.

Everything about this river is epic, from its mythical stories to the extraordinary diversity it spawns.

The Amazon begins high in the Andes, flowing from one of half a dozen known sources.

Other tributaries feed in from Bolivia, Ecuador, Colombia, and Venezuela, forming a massive river system that drains the entire northern half of South America.

The Amazon is at least 6,400 kilometers long, and, incredibly, accounts for 1/6 of all the fresh water on Earth that flows across land to the sea.

People have been living along the Amazon for at least 10,000 years, but the first European to stumble upon it was Don Francisco de Orellana, a Spanish explorer and conquistador.

In 1542, he and his fellow conquerors were searching for cinnamon, and El Dorado, the fabled city of gold.

Instead, they found the greatest river on Earth.

♪ Orellana named the river after the Amazons of Greek mythology, an aggressive tribe of women, who, tall tale or true, cut off their right breasts to improve their archery skills.

Clearly, he must've been intimidated or at the very least, impressed, by the women he met on that maiden voyage down the river, for it still takes the fortitude of a warrior to live in this wild, untamed world.

Despite heavy clearing in recent years, the Amazon basin still holds the largest tract of rainforest on Earth, and, within it, the jaguar's share of our biodiversity.

Every different habitat here provides a home for someone.

Actually, for lots of someones.

In all, there are 40,000 different plants here, supporting millions of insects, hundreds of scaly reptilians, 1,300 bird species, and, making the most of the overhanging branches, a veritable barrel of monkeys.

[Howler monkey calling] The largest and loudest primates here are the howlers.

[Guttural animal calls] Unlike most monkeys, howlers are not colorblind.

Both males and females can distinguish red from green, giving them a great advantage in the forest, for they are able to pick out the younger, reddish, more nutritious leaves when they're foraging.

The slow moving water helps to carry their voices as they communicate to one another.

During the wet season, the Amazon River expands.

In some places, its width swells to 190 kilometers.

It floods whole swathes of the rainforest, leaving many creatures high and dry.

But all that extra water provides researchers and bird watchers with easier access to the jungle and an opportunity to study and document more of this great natural wonder.

♪ While the Amazon is famous for its natural history, the Nile is renowned for its influence on human history, for it gave rise to one of the greatest civilizations on Earth.

In ancient times, the floods of the Nile were said to be the tears of Isis, a mother goddess of Egypt, whose beloved brother and husband, Osiris, god of death and destruction, had been murdered by their evil brother Set.

This flooding occurred on a regular basis, with positive consequences for the ancient Egyptians, nourishing the crops they grew in the flood plains with life-giving water and silt.

The Egyptians' desire to better predict when the river would flood led to developments in astronomy and the creation of the world's first calendar, based on an annual cycle of 365 days.

They also used the river for transporting stone from Aswan, on the southern bank of the Nile, moving it up and downstream on barges to build their great temples and halls.

The banks of the Nile are crammed with monuments and buildings that attest to the mastery of Egypt's artisans, who were able to etch sharp hieroglyphs like these into the stone with all the precision of a laser.

The actual tools they used remain a mystery, but many archeologists suggest it would've been some kind of drill fitted with a cutting jewel that was far harder than the stone itself.

Many historians believe the Nile's timeless cycle, flooding followed by renewal, influenced their belief in the afterlife, a key element in most world religions.

The Egyptians built elaborate tombs and stocked them with furniture, food and wine, and whatever else they thought their dearly departed would need to endure their long journey through the underworld and beyond into the hereafter.

The Egyptians didn't worship the river, as such, but it certainly influenced their worldview, and without it, there's little chance their civilization would have factored so significantly in the shaping of history.

♪ Water plays an important role in many of the world's great religions, but nowhere is it treated with more reverence than India.

The Ganges is India's longest river, flowing 2,500 kilometers from its source in the snowbound Himalaya to the Bay of Bengal.

The Ganges' plains have witnessed the birth of several empires, and continue to support the highest population of any river basin in the world, 400 million souls and counting, a seething mass of humanity that can turn a blind eye to the water's quality in deference to its spiritual purity.

Hindus living throughout the subcontinent believe the River Ganges is sacred, the earthly home of the goddess Maa Ganga.

She is believed to purify everything she touches, absolving those who bathe in the river of all their worldly sins.

The holiest place on the river to pay homage to Maa Ganga is Varanasi, the oldest city in India, if not the world.

Built in the 11th century B.C., it's home to a daunting 23,000 temples and 84 ghats, wide sets of steps that lead to the holy river.

Some of Varanasi's ghats are used for more mundane tasks, such as washing and airing the city's dirty laundry.

Others are pitched perfectly for an impromptu game of cricket.

But Shamshan Ghat, downstream from where the ritual bathing takes place, is sacrosanct.

Hundreds of bodies are cremated here every day in plain sight on pyres that never go out, fueled annually by tens of millions of felled trees.

The faithful believe when their ashes are laid to rest in the Ganges, they escape the cycle of reincarnation, so their souls head straight to heaven.

As India's population continues to grow, pollution increasingly impacts the river, but no matter how severe this pressure becomes, most Hindus believe the Ganges is eternal, remaining forever the heart and soul of India's spiritual life.

♪ At well over 4,500 kilometers, the Mekong is the longest river in Southeast Asia, meandering through six countries, from its source high on the Tibetan plateau to the South China Sea.

The river and its tributaries are the lifeblood for tens of millions of people who live on the water itself... or in overcrowded towns and cities and small rural villages dotted along its course.

Many more depend on the river indirectly, on the rice that is irrigated, and those goods that are traded throughout the whole Mekong Basin.

As the river flows gently through Laos, it also helps to sustain the spiritual life of the people here.

Most practice a form of Buddhism that is still closely tied to their belief in ancestral spirits and animism, the idea that all things, including animals and plants, rivers and mountains, have a spirit or soul.

They see the river as a purifier and life giver, and refer to it in the same way the Hindus refer to the Ganges, calling their river Mae Nam Khong, which means "Mother Mekong."

One of the most respected holy sites on the Mekong is Pak Ou Caves.

For thousands of years, pilgrims have been visiting this great shrine to the river spirit and Lord Buddha, offering prayers, adding to or simply maintaining the thousands of Buddha images inside the cave.

There is a calm here that sets the rhythm to the Lao way of life, masking deep scars left behind by America's secret war, conducted at the height of the Vietnam War, during the '60s and '70s.

When over 260 million cluster bombs were dropped on the country by the U.S.

in an effort to destroy the local Pathet Lao communists and their supply lines, such as the Ho Chi Minh Trail.

A staggering number of missions were flown over a nine-year period, killing a tenth of the Lao population, making Laos one of the most heavily bombed countries in history.

Cu Chi in the Mekong delta was an equally infamous battleground during the post-World War II era.

The Viet Cong used the Cu Chi tunnels as a base for their operations during the Vietnam War, but the building of this vast underground network of hideouts and supply rooms actually began in the 1940s, during Vietnam's war of independence against the French colonialists.

Intense chemical attacks in the Mekong Delta wiped out many of the mangrove swamps that used to protect Vietnam's shorelines from typhoons and tsunamis.

They robbed the soil of its vital nutrients, poisoned the water in the river, and allowed toxic chemicals to enter the food chain.

40 years on, the delta itself appears to be recovering.

Nourished by the fertile silts carried by the mighty Mekong, it's fast regaining its former glory as the rice bowl of Asia.

♪ Often shrouded in mist and, for eons, crowded in mystery, the Sepik is the longest river in Papua New Guinea, a watery thread that stitches a rich tapestry of tribal cultures together.

It is a superhighway for all who live on its shores in one of the most isolated regions on Earth.

The people whose lives revolve around this river speak 250 different languages, but they are bound by a long tradition of trade and cultural exchange.

Their way of life today is little removed from that of their ancestors.

In the middle Sepik region, about half the villages still have a haus tambaran, a traditional meeting place, or ancestral spirit house, where local men gather each day to discuss social and ceremonial affairs or engage in rituals and initiations.

There are tribes here that worship not the river itself but the crocodiles that live within it.

And an important rite associated with their ancestral beliefs involves cutting into the skin of their young men, soothing their fresh wounds with water from the Sepik.

When the scars heal, they're said to represent the teeth marks of the crocodile that has symbolically swallowed the initiates, so that they can be reborn as crocodile men.

[Singing in native language] [Narrator] The cultural wealth of Papua New Guinea reaches a crescendo at the mouth of the Sepik, where sing-sings involving the entire village are becoming more regular, thanks to the smaller, more intrepid cruise ship companies taking guests along the Papua New Guinean coast.

Similar to the dragon dances in China, this heavy costume is borne on the shoulders of 11 men, blindly weaving their way through the village in a traditional ritual to welcome visitors.

The performance allows the villagers to showcase and sustain their culture, passing on their traditions and customs to the younger generation, so they, too, can stay connected to the spirit of the Sepik.

♪ Deep in the rainforest in the southeast corner of Venezuela lies a primordial lost world.

Its jungles are nourished by the thousands of waterfalls that spill from flat-topped tepuis and flow into the Churun River, stained blood red from the tannins that leech from fallen leaves.

Protected by the Canaima National Park, the landscape here incites both reverence and fear.

Legends of monsters and evil spirit beings enliven the local Pemon Indian folklore, and lend their names to key features in the terrain.

They call the Churun River that bleeds through the heart of their homelands "the Traitor," acknowledging the killer current that runs beneath its glassy surface, and they see demonic faces in the rocks that line the Devil'S Throat, a very narrow passage on the river that winds its way towards Angel Falls.

The name of this extraordinary natural wonder is at odds with the rest of the landmarks in the landscape, for it was not named by the Pemon.

Rather, for the explorer Jimmy Angel, who in 1937 crash-landed his plane on top of the Auyán-tepui, the largest mountain casting a shadow over the Churun River.

He, like so many other explorers in South America at the time, was searching for gold, and so, by chance, discovered the falls, the longest single drop waterfall on Earth.

Three times the height of the Eiffel Tower in Paris, it cascades 1,000 meters from the lip of the tepui to the Devil's Canyon below.

For such a huge waterfall, you'd expect the river to be enormous, but on its 36-second journey to the base of Angel Falls, most of the tumbling water that appears to flow in slow motion turns to mist, creating its own microclimate, which contributes to the growth of lush forests below.

The Churun River, however small, flows into the Caroní, one of the largest tributaries feeding the great Orinoco, Venezuela's most significant river.

[Thunder] During the rainy season, when the Orinoco floods, massive shallow lakes form across the plains, creating a haven for water-loving wildlife.

It stretches as far as the eye can see across Los Llanos, the geographical heartland of Venezuela.

There are giant rodents called capybaras, huge iguanas and anacondas, and migratory populations of wading birds drawn by the seasonal flooding.

The scale of Los Llanos is mind-boggling, but it's not the largest tropical wetland in the world created by the flooding of a big river system.

That honor belongs to the Pantanal wilderness in Brazil, which lies in the Upper Paraguay River Basin.

This immense mosaic of rivers and marshes and lakes, covering an area twice the size of Ireland, is basically a vast inland delta.

Supporting such an astounding number of unique plants and animals, it almost rivals the Amazon.

Like most wetlands, the Pantanal is awash with muddy bogs and swamps, but many of the smaller freshwater rivers flowing through the region are as clear as crystal, thanks to the natural filtering properties of limestone, a sedimentary rock that's made up of calcium carbonate.

Limestone-rich hills form the headwaters for many local rivers and streams around Bonito in Brazil.

Its name means beautiful, and it couldn't be more apt.

The water here is extremely clear, allowing schools of dorado and orange-tipped fish to easily tell friend from foe, as they drift with the current through one of the most sublime natural wonders in the world.

♪ The green rolling hills of the North Island of New Zealand conceal another remarkable landscape that owes its existence to limestone and water, Waitomo.

Here, a series of rivers flow far beneath the Earth's surface through a labyrinth of 300 caves.

This natural wonder lures adventurers from all around the globe eager to explore the world quite literally beneath their feet.

Water that enters into cave systems such as this tends to drain downwards through joints and cracks in the rocks, often leaving the water chutes in older caves, which are closer to the surface, high and dry, or just active enough to allow Mother Nature time to continue her handiwork.

The water that still seeps into caverns such as this is slightly acidic and, as it's exposed to the air, its chemistry changes, causing the calcite in the water to crystallize.

Over many thousands of years, these crystals have built up to form stalagmites and stalactites that hang like chandeliers from the ceiling.

When that water hits an impermeable layer, it can't sink any further, and an underground river is born.

The Ruakuri Cave System is one of the longest in Waitomo, and it has a small river of its own that twists its way through a series of narrow passages, slowly widening, as it flows through Earth's version of a block of Swiss cheese.

Only a few creatures can live in total darkness, and this cave system is home to two.

Eels are regularly encountered in the river, and glowworms on the cave walls above.

True, they're just the larva of maggots, looking to attract and snare a meal, but what a wonder they are to behold, as they mimic a star-studded sky.

♪ In the heart of Croatia's Dinaric Alps, close to the Bosnian border, lies the Land of Falling Lakes, an extraordinary stepped river that alternatively cascades and pulls its way through the heart of Plitvice National Park.

It, too, owes its existence to the movement of water underground.

Over millions of years, rainfall on the mountains collected in the porous karst rock, steadily seeping into caverns below.

Over time, the rainwater channeled itself into a gushing subterranean river.

On exiting the maze of caves, this torrent then tumbled through the landscape, depositing tiny crystals of calcium carbonate on anything that got in its way, which eventually built up and petrified to form a particular type of limestone called travertine.

Over the eons, the travertine formed a series of curved dam walls that slowed down the movement of the water, creating the wonder we see here today.

Hundreds of small waterfalls tumble through the forest and spill from the travertine dams.

But even their beauty pales when compared to the luminous aqua blue lakes.

There are 16 in all, and all of them are transparent, which allows their calcified bottoms to reflect light, making the water appear to be blue.

This is an enchanting landscape that continues to slowly evolve, creating formations that will, in time, spawn new lakes and cascades, and even, perhaps, new rivers.

♪ When organic sediments, made up of crushed coral and shell accumulate on the ocean floor, they solidify to form limestone, and when limestone is subjected to intense pressure and heat from deep within the Earth, it transforms miraculously into marble.

19-kilometer-long Taroko Gorge in Taiwan is one of the largest marble canyons in the world, a natural wonder exquisitely sculpted by the thunderous Liwu River.

Marble is an extremely hard stone and doesn't erode easily, which is why Taroko Gorge is so narrow and why it's taken 3 million to 4 million years to form.

What makes this landscape even more of a marvel is the extraordinary feat of engineering that has made access to this natural wonder possible.

In the 1950s, military veterans from Taiwan's nationalist army built the 118-mile Cross-Island Highway in four years.

But 226 of the 19,000 workers lost their lives in rock falls and landslides as they tried to tame the rugged, unstable terrain.

Ironically, part of the shrine that was built to honor those who died while constructing the highway was destroyed by a landslide in 1987, but it was repaired and reopened to the public in the mid-1990s.

Landslides continue to plague the area, and, in particular, the roadway, thanks to heavy rain from typhoons and earthquakes, but fortuitously, many of the better views over Taroko and the tumbling waters of the Liwu can be reached on foot via a series of bridges and narrow pathways, ensuring some form of access for the local monks and nuns who seek to acknowledge the divinity of this great natural wonder year-round.

♪ Many of the oldest rivers on Earth can be found on the driest inhabited continent, Australia.

Scientists using data from remote sensing satellites have recently mapped a network of ancient rivers and streams that once flowed beneath these million-year-old sand dunes in the vast Simpson Desert.

They are still affecting the landscape, providing pathways for the groundwater that feeds small desert lakes.

One ancient river that's still meandering its way through central Australia is the Finke.

Some geologists believe it's been following, more or less, the same course for more than 300 million years.

In most years, it's just a string of isolated water holes, but when it floods, it flows all the way into Lake Eyre, a normally dry salt pan to the south of the Finke.

Where Australia's oldest river systems flow through hilly or mountainous terrain, they carve out spectacular gorges and canyons.

Seasonal rains turn a normally gentle river, such as the Katherine in central Australia, into a force to be reckoned with.

♪ In the dry season, the rapids along the Katherine are deceptively timid, but during the wet, they turn into raging torrents that raise the level of the river by two to three meters in two to three hours, uprooting trees and boulders with frightening ease.

Further downstream, the river's tributaries help the Katherine to pick up her pace, even during the dry, spilling into a series of beautiful rock pools and waterholes before powering into the incredible stone corridor known simply as Katherine Gorge.

This is actually a series of 13 gorges that zig-zag their way through the landscape, where the water flows, in most cases, right up to the sheer cliffs on either side.

Aboriginal people have been visiting or living in the area for tens of thousands of years, leaving behind an artistic record of the way they experienced and interpreted their world.

Their paintings are treasured by the local Jawoyn people, but even they would acknowledge that the river itself is the real master artist here, chipping away at the sandstone and conglomerate for 25 million years.

♪ An even more startling series of gorges in Australia have been cut through the Hammersley ranges in Karajini National Park in Western Australia.

There are more than 20 gorges here dissecting the ancient tableland, and each one is different from the next.

They formed when a sharp drop in sea level tens of millions of years ago caused the rivers running through the ranges to down-cut rapidly.

If you could fast-forward through geological time, those ancient waterways would appear to have sliced through the rock here with all the force of a cleaver attacking a giant slab of layer cake, but the end result is nothing short of spectacular.

The Fortescue River still flows through the ranges, as do other smaller rivulets and streams, leaving behind magnificent pools set like gems in the claws of the Earth.

The contrast of all that wild orange rock against a cloudless blue sky is quintessentially Australian, as are the stark white gum trees and bizarre insects that have made a home for themselves here.

Descending into Weano Gorge using the layers and the rocks as natural steps is like a journey through geological time through thick beds of iron ore laced with blue asbestos that were deposited over two billion years ago.

As the gorge narrows, it really feels like you've ventured to the center of the Earth, only waiting at the end of this sinuous trail is a pool of ice-cold water, rather than boiling hot magma.

♪ Many rivers that flow across the surface of the Earth are fed by Alpine glaciers, huge rivers of ice that push their way down mountains, creating and deepening valleys as they go.

Some mountain glaciers, such as those in Canada's Glacier Bay, end abruptly at the sea.

Others terminate just as suddenly on land, where their meltwaters give birth to rivers.

New Zealand's Dart River flows from the Dart Glacier in the Mount Aspiring National Park.

It's shallow and braided, yet the water within it moves at anything but a glacial pace.

Hidden in the folds of the mountains on either side of the river, waterfalls and streams have worn sinuous chasms into the rocks, becoming mini natural wonders in their own right.

The Dart River flows into Lake Wakatipu, the longest lake in New Zealand, and the Kawarau River flows out of it.

It's not particularly long or significant in terms of water volume, but it is well known for its rapids, bearing alarming names like The Rollercoaster and The Maneater.

Fortunately, there are many other wild rivers on the planet that are less intimidating than the Kawarau, such as the Pieman River, Tarkine wilderness, on the island of Tasmania in Australia.

Many people throughout the world see rivers as a place to unwind.

As they run peacefully through the landscape, providing transportation for services and goods, they also offer us a chance to transport and even transform our souls, a chance to imagine what it must have been like a century or two ago, when many of the wildest rivers on Earth were yet to be discovered or explored.

♪ Of all the explorers who navigated their way into history during the Victorian era, there are few that became as well known as David Livingstone.

He inspired an entire generation on his quest to find the source of the Nile, and even though he failed in that attempt, in 1855, he did discover Victoria Falls halfway along the mighty Zambezi River.

It's impossible to describe this waterfall without resorting to the use of clichés, for it really is an awe-inspiring wonder that leaves most people speechless.

Perhaps the locals sum it up best in the name they give the falls: Mosi-Oa-Tunya, "the Smoke that Thunders."

Sitting on the border of Zambia and Zimbabwe, the falls are over 1,700 meters wide, the largest curtain of water in the world.

More than half a million cubic meters of water plummet over the falls every minute.

That's enough water to fill 200 Olympic swimming pools.

The rock underlying the waterfall is basalt, layer upon layer of lava laid down over one million years.

It sits like an island in the landscape, surrounded by sandy-soiled savanna, and where the water and mist from the falls rain down 24/7, pockets of lush, green forest.

♪ The Zambezi flows through nine countries in total before discharging into the Indian Ocean.

It's one of the few rivers in the world that has remained over much of its course relatively pristine.

The upper Zambezi is world-famous, known to the locals as the River of Life.

Four countries meet at the river at this point, and everyone takes advantage of its flow, for the river nourishes their crops and supports an abundance of good-eating fish.

Perhaps even more significantly, the Zambezi provides a watery corridor for wildlife, which all four nations protect and proudly showcase to the world.

Hippos and crocodiles are regular river guests while lions patrol the banks, and where the Zambezi meets the Chobe River, there are even more animals for the safari guides to show off.

This is where the largest elephant herds in all of Africa come to drink and bathe, keeping pace with the timeless landscape that's been their home for thousands of years.

While most of Africa's great rivers flow out into the sea, the Okavango River empties onto open land, creating an alluvial, or inland, delta.

As it spreads over this vast expanse of the Kalahari Basin, most of the water is either taken up by vegetation or lost to evaporation.

But when the Okavango Delta floods, the wildlife pours in with the water to take full advantage of what suddenly becomes one gigantic seasonal wetland.

♪ Rivers throughout the world outperform many geographical features in the landscape.

They even outdo themselves from time to time, especially when they cascade from cliffs into cauldrons of mayhem and mist.

Niagara Falls straddles the border between America and Canada.

And it has three huge drops that vie for attention, the American and Bridal Veil Falls, and thunderous Horseshoe Falls.

One fifth of the world's fresh water pushes its way over the cliffs here at a rate of half a million liters per second, accompanied by the occasional barrel.

[Announcer] Major Lloyd Hill attempts to shoot Niagara's turbulent rapids, his barrel hammered by rocks, which threaten to split it open.

[Narrator] As bizarre as it sounds, this is what Niagara is best known for, the antics of daredevils who risk their lives, attempting to go with the flow.

Around 5,000 people have died going over Niagara Falls, whether intentionally or by accident.

The chances of surviving are slim.

Even trained stunt people have a one in four chance of dying.

The first person to survive the trip over the falls was Annie Edson Taylor, a 63-year-old schoolteacher from New York.

Motivated by fame and fortune, it didn't turn out to be as lucrative as the Queen of the Mist had hoped, but she certainly did earn her place in the quirkier annals of North American history.

Waterfalls do not have to be the highest or the widest to impress.

They just have to be dramatic, and there are few that fit that bill as eloquently as Iguazu Falls, on the border of Argentina and Brazil.

This astonishing water feature, dividing the Iguazu River into its upper and lower portions, has 275 drops, the largest collection of individual waterfalls in the world.

According to local Gaurani tradition, the falls were created by M'Boy, an angry god who was all set to marry Naipi, the virgin daughter of a local chief.

She didn't want to marry a god and escaped with her human suitor in a small canoe.

When M'Boy discovered what was happening, he was furious and forced the land to collapse beneath their boat.

Naipi was turned into a rock and her suitor, a lonely palm tree.

To this day, when the sun sits at just the right angle, their love takes the form of a rainbow, reaching out to touch one another across the turbulent waters of Iguazu Falls.

Rivers play a significant role in the shaping of all our lives.

They are braided into our mythologies, cultures, and histories.

They feed our bodies and nourish our souls and shape the land around us, and from source to sea, they support a bewildering array of life.

♪