NARRATOR: ONE RIVER DWARFS ALL OTHERS.

THE MIGHTIEST OF THEM ALL.

THROUGH IT FLOWS ONE FIFTH OF ALL THE FRESH WATER ON OUR PLANET.

IT SUSTAINS THE WORLD'S LARGEST RAINFOREST.

IT NURTURES THE GREATEST DIVERSITY OF WILDLIFE ON EARTH... AND INSPIRES VIBRANT CULTURES.

[CHEERS AND APPLAUSE] IT IS A RIVER SO VAST THAT IT DEFIES BELIEF.

IT IS THE AMAZON.

A RIVER OF EXTREMES, SIZE...

TRANSFORMATION, AND COLOR.

TOGETHER THEY CREATE THE SECRET WORLDS AND UNEXPECTED OPPORTUNITIES FOR THOSE WHO MAKE THEIR HOME IN THE LEGENDARY AMAZON.

EARTH'S RIVERS OF LIFE MAKE EXTRAORDINARY JOURNEYS, CARVING THROUGH CONTINENTS, NURTURING GREAT CIVILIZATIONS, FEEDING AND CONNECTING LIFE ACROSS OUR WORLD.

[ELEPHANT GRUNTS] THESE RIVERS ARE THE LIFE-BLOOD OF PLANET EARTH.

NARRATOR: THE STORY OF THE AMAZON STARTS WITH THE SINGLE DROP...

AMONG THE GLACIERS OF THE PERUVIAN ANDES.

HERE, GLACIAL MELT WATER TUMBLES DOWN THE MOUNTAINSIDES.

ON LOWER SLOPES WHERE HUMID AIR FROM BELOW MEETS THE COLD MOUNTAIN ATMOSPHERE...

CLOUD FORESTS GROW, SHROUDED IN MIST.

TINY PLANTS CREATE HANGING GARDENS ON THE BRANCHES OF ANCIENT TREES...

TRANSFORMING WATER VAPOR INTO SPARKLING DROPLETS.

ALL AROUND IS THE SOUND OF THE AMAZON COMING TO LIFE...

THE START OF A 4,000-MILE JOURNEY TO THE SEA.

THE AMAZON IS MADE UP OF MORE THAN A THOUSAND TRIBUTARIES WHICH GATHER WATER FROM ACROSS TROPICAL SOUTH AMERICA...

FLOWING THROUGH 9 COUNTRIES, FEEDING INTO ONE HUGE RIVER WHICH RUNS EAST ACROSS THE AMAZON BASIN INTO THE ATLANTIC OCEAN.

AS IT GATHERS WATER FROM SUCH AN EXTREME AND DIVERSE REGION, THE AMAZON'S HEADWATERS COME IN MANY DIFFERENT SHAPES, SIZES, AND COLORS.

EACH HAS ITS OWN DISTINCT CHARACTER.

ONE SHALLOW AND ROCKY REMOTE AMAZON TRIBUTARY IN BRAZIL PROVIDES AN ENTICING OPPORTUNITY FOR A FAMILY OF ONE AMAZON'S LARGEST AND RAREST PREDATORS... ♪ GIANT RIVER OTTERS.

ADULTS ARE NEARLY 6 FEET LONG.

THIS FAMILY IS EXPLORING A NEW TERRITORY, A 3-MILE STRETCH OF THE CRISTALINO RIVER IN THE AMAZON'S FAR SOUTH.

LED BY DAD, THE FAMILY FOLLOW HIS CALLS WITH A CHORUS THAT IS UNIQUE TO THEIR GROUP.

[GRUNTING] THIS SPOT LOOKS PERFECT, RICH IN FISH.

NOW THE PARENTS CAN TEACH THEIR YOUNG HOW TO HUNT.

IT'S A TESTING TIME FOR THE MOST INEXPERIENCED CUB.

[OTTER CALLING] CALLING OUT A STREAM OF ORDERS, DAD COORDINATES THE HUNTING PARTY.

FISH CAN EVADE OTTERS IN THE DEEP WATERS.

THE FAMILY'S BEST CHANCE IS TO CORRAL THE FISH UP AGAINST THE BANK.

♪ THE YOUNGSTER HAS MISSED OUT.

EVERYONE SEEMS TO HAVE A FISH BUT HIM.

AND HE'S NOT HAPPY ABOUT IT.

LUCKILY, THE FAMILY IS GENEROUS ENOUGH TO SHARE.

NOT THAT DAD SEEMS IMPRESSED.

IT TAKES 3 YEARS FOR AN OTTER CUB TO MASTER THE COMPLEXITIES OF THESE RIVERS.

THE REMOTE HEADWATERS OF THE AMAZON HAVE AN UNPREDICTABLE AND DANGEROUS REPUTATION.

MANY CALL RAPIDS LIKE THESE BOAT BREAKERS.

AND THERE ARE ACCOUNTS OF INTREPID EXPLORERS DISAPPEARING WITHOUT A TRACE.

THESE UPPER REACHES ARE HOME TO THE AMAZON'S LEGENDARY RIVER MONSTERS... LIKE ELECTRIC EELS, CAPABLE OF GENERATING MORE THAN 500 VOLTS...

ENORMOUS PACUS, SOME WEIGHING UP TO 55 POUNDS... AND GIANT ANACONDAS, AMONG THE LARGEST SNAKES IN THE WORLD.

SOME OF THESE AMAZON HEADWATERS ARE SO INACCESSIBLE, THEY STILL HIDE MYSTERIES WHICH ARE ONLY NOW BEING DISCOVERED.

BEYOND THE BANK OF ONE DISTANT TRIBUTARY, THE FOREST CONCEALS A RARE TREASURE.

BRANCHING OFF THE MAIN RIVER IS A POOL OF CRYSTAL-CLEAR WATER... WITH DANCING, BUBBLING SAND.

THIS IS, IN FACT, A SPRING.

RISING FROM DEEP UNDERGROUND, THE WATER IS FILTERED BY THE SAND... LEAVING IT AS SPOTLESS AS AN AQUARIUM.

IT'S FULL OF LIFE, AND WITH SUCH CLEAN, CLEAR WATER, IT'S A PERFECT NURSERY.

A YOUNG COUPLE HAS COME HERE TO RAISE A FAMILY.

A PAIR OF CICHLIDS SO NEW TO SCIENCE, THEY DON'T EVEN HAVE A NAME.

THE FEMALE FINDS A QUIET SPOT TO LAY HER EGGS.

THE MALE FOLLOWS HER TO FERTILIZE THEM IN AN ELEGANT MATING DANCE.

♪ THEY WILL GUARD THEM UNTIL THEY HATCH.

WHEN THEY FINALLY DO, THE YOUNG ARE UNABLE TO SWIM, AT LEAST NOT UNTIL THEY ABSORB THE YOLK SACKS WHICH THEY'RE BORN WITH.

SO FOR NOW, THE PARENTS KEEP THEM SAFE BY HIDING THEM UNDER A LEAF AND DUTIFULLY WARNING OFF ANY WOULD-BE BABY SNATCHERS.

♪ AND LIKE ALL YOUNG PARENTS, SLEEP IS AT A PREMIUM.

A FEW DAYS LATER, THESE BABY FISH CAN FINALLY SWIM... AND LIKE ALL TODDLERS, ARE EAGER TO EXPLORE.

BEING A PARENT IS UNRELENTING, ESPECIALLY WHEN YOU HAVE A BROOD OF OVER A HUNDRED.

♪ CICHLIDS FORM STRONG BONDS WITH THEIR MATES AND ARE AS LOYAL TO THEIR BABIES AS THEY ARE TO EACH OTHER.

BUT OUT HERE, DANGER IS NEVER FAR AWAY.

THE DIFFERENT PROPERTIES OF THE CLEAR WATER SPRING AND THE MAIN RIVER CHANNEL, WHICH IS STAINED DARK BY ROTTING LEAVES...

CREATES A BIZARRE UNDERWATER PHENOMENON... A WATER WALL.

IT'S THE PERFECT HIDING PLACE FOR VORACIOUS MOUTHS-- FRESHWATER AMAZON BARRACUDA AND A LARGE WOLF FISH.

THEY LURK, WATCHING AND WAITING.

BUT THE PREDATORS SEEM STRANGELY RELUCTANT TO ENTER THE CLEAR WATER, FOR FEAR, PERHAPS, OF BEING SPOTTED AND GOBBLED UP THEMSELVES.

BUT WELL-ARMED STINGRAYS ARE BRAVER.

♪ USING THEIR NATURAL CAMOUFLAGE...

THEY CAN SET AN AMBUSH... FROM WHERE THEY MIGHT VACUUM UP THE CICHLID FAMILY IN ONE FELL SWOOP.

THEIR FATE DEPENDS ON THE VIGILANCE OF THEIR PARENTS.

DAD SPOTS SOMETHING... AND DEFENDS HIS BROOD.

♪ THE STINGRAY IS SENT PACKING.

♪ THESE DEDICATED AND BRAVE PARENTS WILL HAVE TO BE EVER-WATCHFUL... SHEPHERDING THEIR YOUNG UNTIL ONE DAY THEY ARE OLD ENOUGH AND BOLD ENOUGH TO FACE THE PERILS OF THE MAIN CHANNEL FOR THEMSELVES.

[ANIMALS CALLING] THE UPPER AMAZON HIDES MANY STRANGE AND SECRET WORLDS TEEMING WITH LIFE, BUT THERE IS ONE REMOTE RIVER IN PERU WHERE THE WATERS ARE SEEMINGLY BARREN.

AS DAWN BREAKS, AN ETHEREAL APPARITION APPEARS, WISPS OF STEAM SNAKING ACROSS THE CANOPY...

REVEALING BELOW, A BOILING AMAZON TRIBUTARY.

ONLY RECENTLY MAPPED, IT IS NOW KNOWN TO BE ONE OF THE LARGEST STRETCHES OF THERMAL RIVER ANYWHERE ON THE PLANET.

AT A TEMPERATURE OF NEARLY 200 DEGREES, ANY FISH UNLUCKY ENOUGH TO STRAY INTO THESE WATERS WOULD BE INSTANTLY COOKED ALIVE.

HOT BEDROCK FROM DEEP WITHIN THE EARTH'S CRUST LIES UNUSUALLY CLOSE TO THE SURFACE HERE, SO THIS WATER IS HEATED AND PURIFIED, WHICH IS WHY THIS STRETCH OF RIVER IS SO SPECIAL.

[MAN CHANTING] NARRATOR: ONE OF 400 TRIBES INDIGENOUS TO THE AMAZON, THE ASHANINKA PEOPLE HAVE BEEN VISITING THE BOILING RIVER FOR GENERATIONS AND REVERE IT FOR ITS HEALING PROPERTIES.

JUAN FLORES IS THEIR SHAMAN.

[FLORES SPEAKING NATIVE LANGUAGE] NARRATOR: JUAN AND HIS FAMILY HAVE DEVELOPED A DEEP CONNECTION WITH THIS PRECIOUS PLACE.

THEY'VE LEARNED THAT BY TAKING PLANTS FROM THE SURROUNDING FORESTS AND MIXING THEM WITH THIS ULTRA-PURE AND SUPER-HEATED WATER, THEY CAN MAKE MEDICINE.

[FLORES CHANTING] [FLORES SPEAKING NATIVE LANGUAGE] NARRATOR: MANY MEDICINES USED TODAY ACROSS THE WORLD HAVE THEIR ORIGINS IN RAINFORESTS, YET LESS THAN A TENTH OF AMAZON'S PLANTS HAVE BEEN STUDIED BY MODERN SCIENCE.

THE REST REMAIN A MYSTERY, KNOWN ONLY TO THE LOCAL HEALERS.

[CHANTING CONTINUES] THIS EXTRAORDINARY RIVER SIMMERS FOR THE NEXT 4 MILES BEFORE IT TUMBLES AWAY FROM THE LAST OF THE FOOTHILLS, DOWN TO THE PLAINS OF THE AMAZON BASIN BELOW.

HERE, THE TRIBUTARIES JOIN TOGETHER AND THE LOWLAND RIVERS BEGIN TO SWELL...

SURGING FASTER AND DEEPER.

THE STRENGTH OF THE CURRENTS ERODES THE SOFT RIVERBANKS.

BUT EVEN FROM DESTRUCTION LIKE THIS, THE AMAZON CREATES UNEXPECTED OPPORTUNITY.

[BIRDS SQUAWKING] HIDDEN TREASURE...

WHICH ATTRACTS GREEN-WINGED MACAWS, WHO FLOCK TOGETHER ON THE NEWLY-EXPOSED BANKS.

THEY HAVE COME TO EAT FRESH CLAY, WHICH MIGHT SEEM STRANGE, BUT THERE IS A VERY GOOD REASON.

THIS PARTICULAR CLAY IS NATURALLY RICH IN SALT, AN ESSENTIAL DIETARY SUPPLEMENT.

FAR FROM THE OCEAN AND LEACHED AWAY BY THE AMAZON'S HIGH RAINFALL, SALT IS HARD TO FIND HERE.

SO THE MACAWS BICKER OVER THE BEST DEPOSITS, CREATING ONE OF THE AMAZON'S LOUDEST AND MOST COLORFUL SPECTACLES.

[MACAWS CALLING] LEAVING THE VERY LAST FOOTHILLS BEHIND THEM, THE LOWLAND RIVERS THEN SET OFF OUT ACROSS THE VAST PLAIN OF THE AMAZON BASIN.

ULTIMATELY, THEY ALL JOIN TOGETHER TO CREATE ONE GIGANTIC MUDDY RIVER CHANNEL.

CLOSE TO THE PERUVIAN CITY OF IQUITOS IS WHERE SOME SAY THE AMAZON TRULY BEGINS.

HERE, OCEAN-GOING SHIPS CAN SAIL NEARLY 2,500 MILES INLAND.

♪ ALMOST HALFWAY THROUGH ITS JOURNEY TO THE SEA, THE AMAZON MEETS ITS MOST DISTINCTIVE AND IMPOSING TRIBUTARY, THE INKY BLACK RIO NEGRO IN BRAZIL.

THE NEGRO IS STAINED DARK BY TANNINS FROM DECAYED FOREST LEAVES, WHICH ALSO MAKE IT ACIDIC.

WHERE THE TWO RIVERS COLLIDE, THEY CREATE ONE OF THE MOST EXTRAORDINARY RIVER SPECTACLES ANYWHERE IN THE WORLD.

IN CONTRAST TO THE NEGRO, THE AMAZON'S WATER LOOKS LIKE CHOCOLATE MILK, HEAVY WITH SEDIMENTS WASHED DOWN FROM THE ANDES.

THE PROPERTIES OF THE TWO ARE SO DIFFERENT, THE LINE BETWEEN THEM CAN REMAIN VISIBLE FOR 90 MILES.

AND IT'S HERE AT THIS GREAT CONFLUENCE WHERE THE AMAZON SUSTAINS ITS GREATEST CITY... MANAUS.

WITH A POPULATION OF OVER TWO MILLION PEOPLE, THIS CITY MADE ITS FORTUNE IN THE 19th CENTURY FROM THE RICHES OF THE RIVER AND SURROUNDING RAINFOREST.

RUBBER, GOLD, AND MINERALS.

THE THRIVING MARKETS OF MANAUS DEPEND ON A CONSTANT SUPPLY OF EXOTIC FOODS.

FOR THE LAST CENTURY, THIS FLAMBOYANT CITY HAS BUILT A REPUTATION AS THE PARIS OF THE TROPICS, DOMINATED BY AN EXTRAVAGANT OPERA HOUSE.

[SHIP HORN BLOWS] THE PEOPLE OF MANAUS DEPEND ON LOCAL FARMERS LIKE EDMAR FERNANDEZ DE LIRA, WHO GROW CROPS ON THE FERTILE MUDDY BANKS OF THE AMAZON JUST OUTSIDE THE CITY.

[SPEAKING NATIVE LANGUAGE] NARRATOR: THESE ARE THE GOOD TIMES FOR EDMAR, BUT HE MUST WORK ALL THE DAYLIGHT HOURS HE CAN.

[DE LIRA SPEAKING NATIVE LANGUAGE] NARRATOR: HERE, THE AMAZON'S BANKS ARE VERY PRODUCTIVE.

ONCE A WEEK FOR 8 MONTHS OF THE YEAR, EDMAR CARRIES NEARLY A TON OF LEAVES DOWN TO THE WAITING BOAT.

[DE LIRA SPEAKING NATIVE LANGUAGE] NARRATOR: BUT TIME IS RUNNING OUT.

THESE ARE SOME OF THE LAST CROPS EDMAR WILL BE ABLE TO SELL FOR MONTHS.

HE MUST PREPARE HIMSELF FOR HUGE CHANGE.

[THUNDER] EVERY YEAR IN NOVEMBER, THE TROPICAL WET SEASON SWEEPS IN.

6 MONTHS OF RAINSTORMS INJECT TRILLIONS OF GALLONS OF WATER INTO THE AMAZON RIVER SYSTEM...

TRANSFORMING IT.

WHOLE SECTIONS OF FOREST ARE WASHED CLEAN BY FLASH FLOODS.

SMALL CREATURES FROM THE FOREST FLOOR HAVE THEIR WORLD TURNED UPSIDE DOWN.

[THUNDER] [ANIMALS CALLING] IN THE MID AMAZON, STRETCHES OF RIVER CAN QUADRUPLE IN WIDTH AND RISE BY 30 FEET.

[ANIMALS CALLING] THE PORT OF MANAUS IS BUILT WITH A HUGE HARBOR WALL TO HELP WITHSTAND THE CHANGE.

BUT BEYOND THE CITY, IT'S A DIFFERENT STORY.

EDMAR'S FARM IS SUBMERGED.

BUT BECAUSE HE HAS PREPARED, HE JUST SHIFTS HIS ATTENTION TO HIS STILT GARDEN.

FOR THE NEXT 4 MONTHS, THE ONLY VEGETABLES TO GROW ON HIS FARM WILL BE THOSE ABOVE THE FLOOD.

BUT WHEN THE RIVER DOES RECEDE, IT WILL DEPOSIT A FRESH LAYER OF SEDIMENT WHICH WILL FERTILIZE A NEW SEASON OF PLANTING.

THE HIGH WATERS LEAVE BEHIND JUST WHAT THE RIVERSIDE FARMERS NEED.

BUT THE FLOODS ARE GETTING WORSE, AND LIVING HERE COMES WITH HUGE CHALLENGES.

[DE LIRA SPEAKING NATIVE LANGUAGE] NARRATOR: IN RECENT YEARS, THE AMAZON HAS FACED MORE EXTREME WEATHER EVENTS... DRIER DRY SEASONS... AND EVEN WETTER WET SEASONS.

WITHIN THE LAST TWO DECADES, RAINFALL HAS BECOME SO INTENSE THAT THE FLOODS HAVE BEEN THE HIGHEST SINCE RECORDS BEGAN.

[SPEAKING NATIVE LANGUAGE] NARRATOR: THE RIVER THAT PROVIDED SO ABUNDANTLY FOR EDMAR AND HIS FAMILY IS NOW THREATENING TO DESTROY THEIR WAY OF LIFE.

IT'S HARD TO SAY WHAT THE FUTURE HOLDS FOR MANY OF THE AMAZON'S RIVER PEOPLE.

ALTHOUGH FOR NATURE, THE EXTREME SCALE OF THESE ANNUAL FLOODS BRINGS INCREDIBLE OPPORTUNITIES.

VAST TRACTS OF LAND BECOME COMPLETELY SUBMERGED, CREATING THE AMAZON'S LEGENDARY FLOODED FORESTS.

NEARLY 200,000 SQUARE MILES OF RAINFOREST BECOMES INUNDATED... A NEW HOME FOR COUNTLESS FISH THAT SHOAL AMONG THE BRANCHES WHERE BIRDS ONCE FLEW.

THE AMAZON HAS OVER 3,000 SPECIES OF FISH.

MANY BREED IN THE FLOODED FORESTS DURING HIGH WATER.

AND HOT ON THEIR TAILS COME THE AMAZON'S MOST REVERED AND MYSTERIOUS CREATURES.

♪ PINK RIVER DOLPHINS, KNOWN LOCALLY AS BOTOS, THE LARGEST RIVER DOLPHINS IN THE WORLD.

[CLICKING] THOUSANDS OF MILES FROM THE OCEAN, THE AMAZON IS THEIR ONLY HOME.

A FLOODED FOREST MIGHT SEEM AN IMPENETRABLE WORLD FOR A DOLPHIN.

HERE, THE FLOODWATER IS STAINED REDDISH BROWN.

SUNKEN BRANCHES CREATE AN OBSTACLE COURSE, BUT BOTOS HAVE THE EQUIPMENT TO NAVIGATE THIS DARK MAZE.

LIKE THEIR OCEAN COUSINS, THEIR DOMED FOREHEAD, THE MELON, ALLOWS BOTOS TO SCAN THEIR SURROUNDINGS USING SONAR.

[CLICKING] THEY CAN NAVIGATE EVERY DROWNED TREETOP WITH ABSOLUTE PRECISION AND HAVE LITTLE PROBLEM LOCATING THEIR PREY.

AND IF THAT'S NOT ENOUGH, BOTOS HAVE ANOTHER TOOL UNIQUE TO THEIR SPECIES.

THEY ARE THE ONLY ADULT DOLPHINS WITH WHISKERS.

[CLICKING] THESE HELP PINPOINT EXACTLY WHERE THEIR PREY IS, NO MATTER HOW IT TWISTS AND TURNS.

[CLICKING] [ANIMALS CALLING] THE AMAZON'S FLOODED FORESTS HAVE EXISTED FOR AT LEAST 8 MILLION YEARS...

CREATING AN EXTREME WORLD SO SPECIAL AND UNIQUE, IT'S THE HOME OF SOME OF THE MOST BIZARRE BIRDS ON EARTH... HOATZINS... WHOSE UNUSUAL LIFESTYLE SETS THEM APART.

FOR A START, THEY FEED ALMOST EXCLUSIVELY ON LEAVES, A DIET WHICH HAS AN UNFORTUNATE AND GASSY EFFECT ON THEIR DIGESTION, LEADING TO THEIR NICKNAME, STINK BIRDS.

DURING THE FLOOD SEASON, CERTAIN RIVERSIDE PLANTS BURST INTO A FLUSH OF NEW GROWTH.

IT'S THE TIME FOR HOATZINS TO BREED.

BUT THE NEW LEAVES ATTRACT SPIDER MONKEYS, TOO.

SOME MONKEYS CAN BE A THREAT AND OFTEN EAT EGGS THEY FIND.

HOATZINS ONLY SAFETY IS IN THE MOST INACCESSIBLE BRANCHES CLOSE TO THE SURFACE OF THE RIVER...

SAFE FROM THE REACH OF GREEDY MONKEYS, BUT NOW IN DANGER FROM THE FLOODWATER.

[THUNDER] EVEN NEAR THE END OF THE AMAZON'S WET SEASON IN MAY, SUDDEN, INTENSE STORMS CAN BRING OVER 3 INCHES OF RAIN IN A DAY... DROWNING ANY NESTS BUILT TOO LOW AND BRINGING OTHERS IN REACH OF RIVER PREDATORS... LIKE THE BLACK CAIMAN.

TO MAKE THE SITUATION EVEN WORSE, HOATZIN CHICKS ARE CURIOUS AND A LITTLE CLUMSY.

FORTUNATELY, THEY'RE NOT TOTALLY HELPLESS... BECAUSE THEY'RE BORN WITH A PIECE OF CLIMBING EQUIPMENT VERY FEW BIRDS POSSESS... CLAWS ON THEIR WINGS.

♪ SO EVEN THIS LITTLE INFANT CAN CLIMB BACK UP TO SAFETY.

AT THE RAINY SEASON'S PEAK, NEARLY 300,000 SQUARE MILES OF THE AMAZON'S FLOOD PLAIN ARE SUBMERGED.

UNDER THIS COLOSSAL WEIGHT OF WATER, THE EARTH'S CRUST CAN SINK BY 3 INCHES.

THE FLOODWATERS CAN REMAIN HIGH FOR 3 MONTHS, BEFORE THEY FINALLY DRAIN AWAY DOWN INTO THE LOWER AMAZON IN NORTHEASTERN BRAZIL.

HERE IN ALTER DO CHAO, RIVERBANKS CAN BE NEARLY 15 MILES APART, LITERALLY OVER THE HORIZON.

STRETCHES OF THE LOWER AMAZON LOOK MORE LIKE A SEA, AND ON ITS SHORE THERE ARE SOME SPECTACULAR BEACHES.

THIS REGION IS OFTEN CALLED THE CARIBBEAN OF THE AMAZON...

EVEN THOUGH IT'S STILL OVER 300 MILES FROM THE OCEAN.

EVERY YEAR, CROWDS OF RIVER PEOPLE, THE RIBEIRINHOS, GATHER HERE FOR A SEASONAL CELEBRATION OF THE RIVER.

♪ AS THE PARTY PREPARATIONS BEGIN IN THE TOWN, SANDRO BRANCO AND HIS GRANDFATHER ENJOY A MOMENT OF QUIET BEFORE THE FIESTA.

[SPEAKING NATIVE LANGUAGE] NARRATOR: SANDRO IS RIGHT TO BE NERVOUS, AS ALTER DE CHAO STAGES ONE OF THE MOST COLORFUL AND SURPRISING RIVER CARNIVALS IN ALL BRAZIL, AND THIS YEAR SANDRO IS THE LEADING MAN.

[BRANCO SPEAKING NATIVE LANGUAGE] ♪ [CROWD CHEERING] NARRATOR: SANDRO IS THE STAR OF THE SHOW, PLAYING THE PINK BOTO, A LEGENDARY CREATURE FOR THESE RIVER PEOPLE.

THE LOCAL LEGEND IS THAT ON THE NIGHT OF THE FULL MOON, THE BOTO DOLPHIN TURNS INTO A HANDSOME AND SEDUCTIVE MAN WITH A HAT AND A WHITE SUIT.

ONCE ON LAND, HIS CHALLENGE IS TO SEDUCE YOUNG WOMEN.

[CROWD CHEERING] DESPITE THE PRESSURE...

THE DANCE HAS BEEN A SUCCESS.

[BRANCO SPEAKING NATIVE LANGUAGE] NARRATOR: SANDRO IS THE THIRD GENERATION OF BOTO DANCERS IN HIS FAMILY, BUT HE'S FACING STIFF COMPETITION.

THE NEXT WAVE OF TALENT IS HOT ON HIS HEELS.

[BRANCO SPEAKING NATIVE LANGUAGE] NARRATOR: THIS IS A CELEBRATION THAT HAS BEEN GOING ON FOR HUNDREDS OF YEARS...

REVEALING HOW THE LIFE OF THIS GREAT RIVER AND THE LIVES OF MILLIONS THAT LIVE ALONG ITS BANKS ARE INEXTRICABLY INTERTWINED.

ON THE COAST OF BRAZIL, MORE THAN 4,000 MILES FROM ITS SOURCE, THE AMAZON RIVER FINALLY REACHES ITS MOUTH.

IT'S HERE THAT JUST A FEW TIMES A YEAR THE LARGEST AND PERHAPS MOST DANGEROUS MONSTER OF THE AMAZON SHOWS ITS FACE.

[MAN SPEAKING NATIVE LANGUAGE] NARRATOR: THE POROROCA IS SO LARGE, IT IS HEARD BEFORE IT IS SEEN.

THE VERY NAME ITSELF MEANS GIANT ROAR.

[MAN SPEAKING NATIVE LANGUAGE] POROROCA!

♪ NARRATOR: ON A FULL MOON, THE TIDE FROM THE ATLANTIC IS SO STRONG THAT ITS WATER SURGES INTO THE AMAZON RIVER CHANNEL, TEMPORARILY REVERSING THE FLOW OF THE GREATEST RIVER ON EARTH...

CREATING ONE OF THE MOST IMPRESSIVE TIDAL BORES IN THE WORLD.

[MAN SPEAKING NATIVE LANGUAGE] ♪ NARRATOR: BUT THE BEAST IS NOT FEARED BY EVERYONE.

[MAN SPEAKING NATIVE LANGUAGE] NARRATOR: FOR SERGENIO LAOS, THE POROROCA BRINGS A TRULY UNIQUE OPPORTUNITY TO SURF THE AMAZON.

♪ [LAOS SPEAKING NATIVE LANGUAGE] ♪ NARRATOR: WHEN THE POROROCA EVENTUALLY SUBSIDES, THE AMAZON COMPLETES THE FINAL LEG OF ITS JOURNEY...

IN THE ATLANTIC OCEAN.

♪ HERE THE AMAZON SPREADS OUT AS A VAST CLOUD OF MUDDY WATER, WHICH CAN COVER AN AREA OF SEABED THE SIZE OF TEXAS.

UNTIL RECENTLY, IT'S BEEN VERY DIFFICULT TO FIND EXACTLY WHAT LIES AND LIVES BENEATH.

BUT TODAY, THE VERY LATEST TECHNOLOGY AND THE MOST ADVANCED SUBMARINES ARE ALLOWING SCIENTISTS TO EXPLORE THIS HIDDEN WORLD.

♪ ON A DIVE 300 MILES FROM THE AMAZON'S MOUTH, THE EXPEDITION IS REVEALING THAT THE RIVER'S NUTRIENTS ARE FERTILIZING THE OCEAN'S WATERS, CREATING A BLOOM OF PLANKTON.

IT'S HARD TO IMAGINE THAT THERE WOULD BE LIFE UNDER THIS MURK.

AS THE DIVE CONTINUES BELOW THE PLUME, CHIEF SCIENTIST RODRIGO MOURA AND PILOT ALAN SCOTT DISCOVER SOMETHING EXTRAORDINARY.

SCOTT: WOW, I'VE EVER SEEN ANYTHING LIKE THIS BEFORE.

NEVER.

NARRATOR: A MASSIVE REEF OF STRANGE, ROCK-LIKE ALGAE... OH, LOOK.

JACKS.

LOOK AT THE SIZE OF THESE GUYS.

NARRATOR: EXPLODING WITH RICH AND VARIED MARINE LIFE.

MOURA: ANGELFISH HEAVEN.

NARRATOR: UNDER THE DENSE PLUME OF THE FERTILE RIVER WATER, IT TURNS OUT THERE'S A HIDDEN WORLD-- AN ENORMOUS REEF MORE THAN 600 MILES LONG.

INSTEAD OF CORAL, THE UNIQUE PROPERTIES OF THE AMAZON HAVE CREATED A GARDEN OF GIANT SPONGES.

♪ SOME OF THE SPONGES ARE MORE THAN 3 FEET ACROSS AND A THOUSAND YEARS OLD, ALL FEEDING ON NUTRIENTS WHICH THE AMAZON HAS COLLECTED ON ITS INCREDIBLE JOURNEY.

♪ FOR THE SCIENTIFIC WORLD, THIS IS TOTALLY UNEXPECTED.

MOURA: YOU DON'T SEE THIS EVERY DAY, HUH?

NO, NOT EVERY DAY.

THIS IS SPECIAL.

NARRATOR: NO OTHER RIVER ON EARTH IS KNOWN TO HAVE THE POWER TO SHAPE SUCH AN EXTRAORDINARY ECOSYSTEM OUT IN THE OCEAN.

EVERY DIVE IS NOW REWRITING TEXTBOOKS.

A RIVER OF THIS SCALE HAS GREAT EXTREMES, FROM TINY DROPS IN ICY MOUNTAINS TO THE GREATEST ANNUAL FLOOD ON EARTH.

FROM CRYSTAL CLEAR POOLS TO GIGANTIC PLANKTON BLOOMS, THE EXTRAORDINARY POWER AND STRENGTH OF THE MIGHTY AMAZON CREATES INCREDIBLE CHALLENGES AND FANTASTIC OPPORTUNITIES FOR ALL WHO CALL THIS GREAT RIVER THEIR HOME.

ANNOUNCER: TO ORDER "RIVERS OF LIFE" ON DVD, VISIT shopPBS, OR CALL 1-800-PLAY-PBS.

THIS PROGRAM IS ALSO AVAILABLE ON AMAZON PRIME VIDEO.

♪