[Birds chirping] ♪ Narrator: At the top of North America is a legendary river... flowing through some of the most remote country on Earth... a last frontier, where the call of the wild is still strong.

For thousands of years, its riches have sustained the First Nation people living along its banks.

From vast ice fields and great lakes... to endless forests and tundra plains, it gathers its waters... and brings life wherever it touches.

[Birds chirp] Relentless.

Immense.

It seems all-powerful, but another force is at work here-- the cold of the Arctic winter.

When it strikes, this river is transformed.

It becomes a river of ice... a frozen highway upon which many will depend during the long, dark winter.

From free-flowing giant... to icebound lifeline, this is the Yukon, North America's great frozen river.

♪ Earth's great rivers... make extraordinary journeys... carving through continents... feeding and connecting life... nurturing culture... providing a place for adventure.

♪ From the frozen wilderness of the Yukon... to the tropical heat of the Zambezi... [Grunts] and the magical, hidden worlds of the Danube... ♪ rivers are the lifeblood of planet Earth.

♪ Narrator: For 2,000 miles, the Yukon River flows in a great arc through northwest Canada and central Alaska to the Pacific Ocean.

Along the way, it gathers water from 320,000 square miles of wilderness, an area larger than Texas.

The Yukon story begins deep in the coastal mountain ranges of British Columbia.

The Juneau icefield, 1,500 square miles and nearly a mile deep.

The flood of summer meltwater from these glaciers fuels the Yukon on its journey to the sea.

But this far north, the seasons change quickly.

As autumn temperatures plummet below zero, the Yukon's tap turns off.

[Ice crackling] Soon, the entire river is hidden beneath a shield of ice.

But despite the October chill, one of the Yukon's remote tributaries remains ice-free.

In Fishing Branch River, thermal springs percolate from deep underground, warming the stream just enough to keep it flowing.

This creates an opportunity for some of the Yukon's toughest characters.

For weeks, chum salmon have been battling their way upstream from the Pacific.

Racing the freeze, they have swum over 1,500 miles, following a long-remembered scent to reach their spawning beds in this stream.

On arrival, the females excavate shallow scrapes, or "redds," in the gravel.

Around them, the hook-jawed males tussle for prime position.

They need to be close to fertilize the thousands of eggs the females release into their nests.

But spending so much time in the shallows leaves them vulnerable.

[Roaring] Up to 40 grizzly bears visit the creek during the brief spawning season.

With air temperatures at 30-below, wet fur quickly freezes, coating the bears in frost.

[Huffs] [Growls] These are the Yukon's ice bears, unique because the late salmon run means they can still hunt when other grizzlies are already hibernating.

These cubs lack the pioneering spirit... but their mother doesn't.

[Roars] [Grunts] She keeps the first catch of the day for herself.

[Grunting] But her cubs are hungry and determined not to miss out on breakfast.

They just need to find a way across the river.

Too slow.

Mom is straight back into the stream... chasing a second breakfast.

When her direct attack doesn't work, she gently paws the water, encouraging the salmon into the shallows, where they can be picked off.

When the fishing is good, she will eat 70 pounds every day, feasting on the juiciest, energy-rich parts like eggs and skin.

[Huffs] But as the run dwindles, even old fish heads start to look appetizing in the rush to put on enough weight to see them through the winter.

[Grunting] After a hard day's fishing, a good scratch helps them defrost.

♪ Once the fish are gone, even these tough ice bears will retire to their dens to hibernate for the winter.

[Distant bird chirps] As the Northern Hemisphere faces away from the sun, an intense cold now settles along the Yukon.

Across northern Canada and Alaska, the Yukon is locked away beneath several feet of ice.

It will stay frozen for 6 months or more.

Temperatures tumble to -50 degrees.

As winter blizzards sweep along the Yukon valley, the hard river ice is blanketed by snow.

In a land with few roads, the frozen river becomes a highway through the forest.

[Dogs barking and howling] And the skills needed to run these ice roads still flourish along the Yukon.

[Whines] [Dogs barking] Woman, voice-over: I've been traveling on the river my whole life.

Hayes: Kyla Boivin is a dog-sled racer, and the frozen Yukon is her racetrack.

Kyla, voice-over: I like how it all changes from mile to mile.

The land is so big.

It's the highway of the North, right?

Hayes: She's putting her top team through their paces along a section of the Yukon Quest Challenge, a sled race billed the toughest on Earth.

It's a 1,000-mile test of endurance and teamwork, run between Whitehorse in Canada and Fairbanks in Alaska.

[Wind howls] Kyla has tackled this marathon 7 times, the first when she was just 18 years old.

Now she rides just for the thrill of it.

[Dogs howling] The race harks back to the time when the frozen Yukon was the only link between isolated settlements and the outside world.

Kyla, voice-over: Temperatures can be 50-below.

You can have a blizzard where it drops 8 inches of snow and the trail is gone.

There are spots that are just windswept, and it's barren and it's like the moon down there.

Hayes: Kyla is following that same call of the wild that drew the early pioneers to the Yukon.

Kyla, voice-over: You're only gonna have 6 hours of daylight [chuckling] in the--in the winter, right?

In the deepest winter.

And when it's dark, you only see your headlamp beam.

That's not very far to spot trouble.

You are completely relying on the dogs, and they are completely relying on you.

And they're such wonderful creatures.

They're my favorite creatures on this planet, the sled dogs.

[Chuckles] Definitely.

Hayes: Even today, life for a musher and dog team out on the ice is much the same as those pioneering days.

Some straw for the dogs and a fire to melt snow for coffee can make life a little more comfortable.

[Whines, yelps twice] It's bitter, 25 below.

[Exhales sharply] They're good dogs.

Once they see the straw, usually--these guys have camped a lot, so they know straw means we're staying awhile.

[Whines] [Distant animals calling] Hayes: Despite the cold, the frozen river is a lifeline through these northern forests.

Even in deep midwinter, lynx are on the prowl.

Using the windswept ice river means they can avoid deep, energy-sapping drifts.

[Wind howling] [Birds chirping] Their huge, furry paws act as snowshoes, helping them move effortlessly across soft snow.

[Distant birds squawking] Lynx are top predators... but a half-ton moose is way out of their league.

They have something much smaller in their sights.

Snowshoe hares can make up 90% of their winter diet... but being a specialist hunter brings its own problems.

Hare numbers rise and fall dramatically in regular ten-year cycles, and in years with few hares, many lynx starve.

[Growls softly] Even in good years, pursuing such elusive prey means covering many miles every day.

As they wander these well-traveled highways, lynx mark out their territories... [Splattering] with a squirt here... and a squirt there... leaving scent to help stake their claim to a stretch of frozen river and to advertise for a mate.

These chemical signposts are the only way these loners can keep in touch in such remote country... and this really is North America's wild frontier.

Along the Yukon, there are no big cities and few roads.

Only 4 bridges span its 2,000-mile course.

Just 125,000 people live in the entire Yukon Basin.

400 miles east of Anchorage, close to the Alaska-Canada border, is one of the few riverside towns-- Dawson City... where the Yukon is joined by its most famous tributary, the Klondike River.

Dawson sprang up almost overnight after gold was discovered here in 1896.

By the following year, gold fever had lured 30,000 fortune hunters to this remote riverbank.

A lucky few struck it rich.

Most left emptyhanded, defeated by the Yukon's crushing hardships.

In just a few years, the gold petered out and the rush was over.

[Wind howling] But Dawson lived on, a beacon of light in a sea of wilderness.

One of the strangest reminders of those wild times can be found in the Downtown Hotel Saloon, where the preserved, frostbitten toe of a Yukon prospector has become the key ingredient in a unique cocktail.

Taking the Sour Toe Challenge has become a rite of passage for anyone who visits Dawson today.

Man: And if you dare, we can serve the toe.

Are you ready?

[Woman chuckling] I guess so.

Man: You'd better be 'cause here we go.

You can drink it fast, you can drink it slow, but your lips must touch this gnarly toe.

Just your lips-- no teeth, no tongue, no tonsils.

Sláinte.

Heh heh!

Should I just do it?

Oh.

Oof.

Man: You got it!

[All clamor] That was well done.

That was well done.

[All laughing] Perfect.

One.

[All laugh] [Distant dog barking] Hayes: Just when it seems the cold will never release its grip on the Yukon, there's a sign in the heavens that change is coming... the aurora borealis, the Northern Lights.

These atmospheric lightshows often reach their dramatic peak just as the Earth's orbit swings the Northern Hemisphere back towards the sun.

[Distant birds squawking] It marks a moment of transformation as new energy pulses along the Yukon.

Rising temperatures and the stirrings of long-dormant currents open the first breaches in the frozen river's defenses... just in time to greet thousands of noisy migrants to the Yukon.

[Scattered honking] Trumpeter swans have flown over a thousand miles from southern Canada en route to their breeding grounds further north.

Marsh Lake gives these huge birds a chance to rest and refuel, but only if their timing is spot-on.

If they arrive before the thaw, ice stops them from feeding on the sedges that grow on the lakebed.

Arrive too late, and spring floods put these plants beyond reach.

They've got it just about right, although the cold April nights still glaze over the open water, so the early risers must help break the ice.

Even for these long-necked birds, it's a stretch to gather the vegetation 3 feet down.

[Cheeping] Unable to reach the plants for themselves, smaller migrants like wigeon stick close to the swans, scooping up any leftovers.

Rested and refueled, it's time to move on, chasing the spring thaw as it moves north.

♪ It takes a while for the thaw to reach the Yukon's Arctic tributaries.

Even in May, these are still frozen solid... rivers like the Porcupine.

500 miles long, its course takes it north, across the Arctic Circle, then back south to join the Yukon.

At its most northern point is the First Nation Vuntut Gwitch'in village of Old Crow.

Here, life revolves around subsistence-fishing and hunting.

Man: Winter in Old Crow can be harsh, it can be cold.

Being above the Arctic Circle, we--we experience earlier winters and-- and later springs.

The Porcupine River is the last-- one of the last large rivers to break up and--and that's where we're at right now.

Hayes: Every day, Paul Josie climbs the bluffs above the village to scan the frozen river.

Paul: As I stand and witness the changes in front of me from the river, and you hear the geese in the sky and the water trickling down the mountain, and you can feel the warm air on your face, it gives me a sense that spring will be upon us.

Hayes: There's one sign, above all, that means spring is close... the arrival of the Porcupine caribou herd... over 200,000 animals on the move... [Caribou grunting] a 1,500-mile migration, the longest by any land mammal on the planet... taking them to their calving grounds on Alaska's Arctic coast.

Early arrivals at the still frozen Porcupine River, mainly the pregnant cows, simply walk across the ice.

[Creaking] [Distant rumbling] But temperatures are rising rapidly.

Melting ice eases away from the banks and starts to break up.

Now, as more caribou arrive, they face a dangerous, shifting patchwork of unstable ice and open water.

[Caribou grunting] There's no way through.

They're forced to wait as a growing mass of ice surges downstream, towards Old Crow.

[Crunching] Slabs of ice jam against one another, blocking the river.

Some caribou get caught out, marooned as the ice breaks up around them.

[Caribou grunting] The lucky ones are carried back to shore, miles further downstream.

Ice continues to build around Old Crow until the pressure can no longer be contained.

Miles of river ice stream past, heading for the Yukon.

Paul, voice-over: Ever since I was young, the break-up of the river has always been an exciting time for my community.

Watching the break-up is literally watching winter wash away.

Hayes: The remaining caribou take their chances amongst the ice.

Paul: Watching the Porcupine caribou swim across the river, navigating through ice chunks... [Caribou grunting] you get a sense of worry for this animal, as you-- you want them to succeed, you want them to cross, and you want them to be safe.

[Caribou grunting] Hayes: As the Porcupine ice disappears downstream, the last of the caribou make their way across the river, playing catch-up with the rest of the herd.

Paul: Now that the river has broken up, um, it's actually... just waiting for more ice to clear, waiting for it to be a little safer to travel... [Ice creaks] and then we can put my boat in and start traveling on our highway again.

Hayes: After months of isolation, the inhabitants of Old Crow can finally reconnect with the Yukon.

[Birds chirp] From here on, the river turns its back on the Arctic and sets a course for the ocean.

[Grunting] Bathed in near-continual summer daylight, the great frozen river comes alive.

[Screeches] The snow and ice that brought the Yukon to a winter standstill now re-energizes the river.

[Screeching] With every stream and tributary adding its own pulse of meltwater, the Yukon's power steadily grows.

With the flood comes something just as important as the water... an ever-growing cargo of rock dust from distant glaciers and mud from eroded valleys.

♪ This meltwater turns the Yukon into a formidable and relentless giant.

Over the short summer, the river will shift more than 80 million tons of sediment... most of it carried all the way to the ocean.

This unique mineral signature helps guide waves of salmon back to the Yukon.

Runs of chum, coho, pink and king salmon battle their way hundreds of miles upstream to spawn in the river's headwaters.

For thousands of years, the indigenous First Nation people harvested the fish, a summer bounty that fed them through the winter.

It's still a tradition for families to head to remote riverside fish camps to catch and prepare salmon.

From the Athabascan First Nation, sisters Faith Peters and Kathleen Peters-Zuray are heading to their camp at Rampart Rapids.

Faith, voice-over: I'm Middle of the River clan, and we've been surviving on king salmon all our life.

We've been coming to fish camp here for, like, 35 years.

Hayes: Over those years, the sisters have witnessed dramatic changes along the river.

Recently, the Yukon's many salmon runs have gone into steep decline, victims of a shifting climate and over-fishing in the Pacific.

Strict limits are now placed on catches, and if numbers of returning salmon are very low, no fishing is allowed.

The family wait for this summer's decision, relayed via the local Mukluk radio station.

Male announcer: The pre-season projection does not meet the threshold of 300,000 fish needed to allow subsistence-fishing, therefore subsistence salmon-fishing will be closed to begin the fall season.

Subsistence fishermen should prepare for continued closures.

Hayes: Despite this bad news, the sisters are determined to keep up the traditional knife skills they learned as children.

Kathleen, voice-over: It's hard for us not to come to fish camp and to cut fish, 'cause this is what we've been doing all our life.

Hayes: With no fresh fish to cut, Kathleen retrieves what's left of last year's catch from the camp freezer.

Ooh.

There you go.

We're ready.

This is one of the salmon that was in the freezer from last year, so it's a little soft, but it's still beautiful.

Faith, voice-over: It's not even a job for us to do this.

It's a happy vacation.

Hayes: The strips are hung in the breeze to dry.

Faith: It's amazing that you're-- we're using frozen fish... and it's turning out pretty good.

Gonna taste like gold.

Hayes: After a day in the sun, the oil-rich strips are moved into the smokehouse.

The smoke helps preserve the fish by creating a coating that slows decomposition.

In past years, this smokehouse would be full to the rafters with salmon.

These few strips are a sad reminder of how bad things have become.

Kathleen: So there was no summer chum, no king, and no fall chum.

That is... unprecedented.

We've never seen that.

It makes me sad, it really makes me sad because... for us to have a dinner without king salmon, it's almost like starving.

It hasn't really hit me, really, but we're losing, um, a part of our culture.

Um, it's... it's devastating.

Hayes: The sisters can only hope next summer brings more salmon back to the Yukon so they can fill the smokehouse once again.

[Animals calling] By September, autumn is coloring the Yukon's banks.

Bull moose are putting the finishing touches to something remarkable.

[Huffing] Every year, they grow a new set of antlers.

In older bulls, these can be 6 feet across and weigh 50 pounds.

[Grunts] Bulls need top-quality grazing to grow these huge racks, and lots of it-- over 35 pounds every day.

Up to half their summer diet consists of water plants, rich in protein and vital bone-growing minerals.

At their peak, the antlers are growing at almost an inch a day, making them the fastest-growing organ in the animal kingdom.

All this effort is just for one thing-- to get noticed, and this bull's eye-catching headgear has already done its job.

[Snorts] All he needs to do now is dig a pit and soak the soil with his scent, releasing pheromones that add to his already impressive allure.

[Urine squirting] [Grunts] [Sniffing] He's irresistible.

[Distant animal calling] Now over half a mile wide and still 700 miles from the sea, the mud-filled Yukon swings southwards... into some of the wildest country in Alaska.

With no roads or rail links, the few isolated villages here rely on the Yukon to stay connected to the wider world.

Bush pilots can make some deliveries... while anything bulky must be carried by barge.

Man: This is the last run of the season.

We do about between 13-- maybe even 14,000 miles, river miles, transporting cargo for customers.

Hayes: Barge Captain Lester Hakey has been working on the Yukon for 26 years and knows this autumn voyage is risky.

Lester: Most of the challenges are the, uh, river depth.

That's the biggest challenge.

Hayes: It's only September, but the headwater streams that feed the Yukon are already starting to freeze, slowing the flow of water into the main channel, and river levels are dropping.

Lester: You got big river, you got wide river, but you still have channels where the river will go from 35 feet to 6, 7, 8 feet, you know, and then you can get yourself stuck down there.

Hayes: The currents are incredibly powerful, testing the crew's skill as they maneuver their way downstream.

And the barge doesn't stop just because the sun goes down.

Lester shares the piloting with Sean Wright.

It's 6 hours on, 6 off, around the clock, 7 days a week.

Sean: The Yukon River's not charted.

You won't see any navigational aids like you will anywhere else in the lower 48.

You can go on any river down there, you're-- most part, you're gonna see buoys, red and green.

Out here, there's nothing.

Um, we use trees.

There's plenty of trees that I use.

There's valleys in the mountains that I look at.

Uh, there's a lot of landmarks that just come from, you know, years of driving on the river.

Hayes: As the Yukon snakes its way deeper into the wilderness, the barge repeatedly crosses from bank to bank, seeking out the deepest water.

But these channels, or holes, are constantly shifting as the current builds new mud banks and bars.

To find a way through, Lester must take a closer look.

Lester: The end of the season, yeah, sometimes the Yukon River may drop 2 or 3 feet in 24 hours.

So what we're doing here is we're trying to sound a hole, a good hole to get the-- get the, uh, tug through the barges.

This used to be a really easy crossing, but now it's, uh, it's one of the more difficult ones here on the--that we're doing right now on the Yukon River.

See there, 6s and 7s?

You have 6s and 7s on the Yukon River, uh, you're in the wrong place.

There are some 6s, 5s.

Navigating in the deepest water that you can.

If you continue to try to follow around a bend, and the water's taking off the other way, you're gonna drive right into a bar that's underwater.

Lester: If you look right here, there's a piece of drift?

That tells you the channel's coming this way, and you got to thread the needle and get over to the bluff.

Sean: It can be deceiving, too.

You can think you're going into a good crossing, and it's not.

If something's questionable, we'll put the sounding boat in and we'll figure out the channel.

Hayes: Finally, the depth gauge climbs to 30 feet.

Lester: And I think we got her.

I think we'll have it.

Hayes: With the dangerous shallows safely behind them, the barge plows on downriver, and the crew get ready to make the crucial autumn deliveries.

Sean: There's really nothing that we won't move.

Um, if-- if it's got wheels or if it can be picked up by heavy machinery, we will--we will haul just about anything that you can bring us.

We've got excavators, loaders, we've got 70-foot-long conveyor belts on trailers.

Yep.

Lester on radio: Keep on rolling, son.

Looking good.

Hayes: And with no docks or piers in the villages, deliveries are unloaded down makeshift ramps.

Sean: Uh, we've got people's personal vehicles.

Man: Thanks a lot.

Lester: All right, dude.

All I do is get it from point A to point B, man.

Oh, yeah.

Yeah, here you go.

[Ship's horn blows twice] Sean: Uh, people's food, groceries, soda cans, uh, building materials-- yeah, just about anything you can think of.

Hayes: If anything's been forgotten, it's 8 months before the spring thaw allows deliveries again.

The barge's most precious autumn cargo is 180,000 gallons of oil.

It's what villagers rely on to warm their homes and run their vehicles once winter comes.

Lester: I love the challenge.

I love the challenge of the whole thing.

It's just, uh, it's--it's awesome because when you get done, and you--you're, you know, you think you've been beat, and then, all of a sudden, you're-- [whistles]--you get it done and everybody's happy and you got the freight off to the people and they're happy and... you feel a sense of accomplishment, you know?

Yeah.

That's part of the reason why I love this, you know?

I mean, you can't beat this office to work in, can you?

Ha ha!

I mean, really.

Hayes: After the last delivery, it's an 8-day battle back upstream to their winter quarters before the river freezes.

Meanwhile, the Yukon, now at its widest and most remote, forges westwards into a very different world.

[Wind blowing] With the mountains left far behind, there's almost no gradient left to drive the river forwards.

Across this flat, exposed landscape, the Yukon slows and spreads, splitting into a tortuous network of meandering channels.

Breaking up this maze of waterways is an endless, boggy tundra.

This is the Yukon Delta.

Covering over 50,000 square miles, it's bigger than the state of Louisiana and one of the largest deltas on the planet.

At the very end of its journey, the Yukon has one final surprise.

Rising out of the waters surrounding the southern delta is Nelson Island.

Here, at the very edge of the continent, live some remarkable creatures.

[Grunting] Muskox.

With their fine, woolly coats, these relics of the last Ice Age can shrug off the very worst delta weather.

Days are spent gathered in small family groups, a tight-knit sisterhood of cows with their calves and one very large bull.

He's trying his best to corral the wandering females, constantly checking if any are ready to mate.

It's the rutting season, and his harem has caught the eye of a young bull, who fancies his chances.

As the herd drifts over the hills... the hopeful youngster follows, slowly getting closer.

Finally, his presence forces the resident bull to react.

Encounters like this are all about intimidation... as rivals assess each other's size and strength.

[Grunting] A few tentative shoves, and this youngster quickly realizes he's more than met his match.

During the rut, contests like this are kicking off all across the tundra.

If rivals are evenly matched, things can escalate into a full-blooded confrontation.

♪ Thick skulls and 4-inch horn bosses act like helmets, protecting them from these earth-shaking collisions.

Intruder seen off, the victor has won the chance to father next year's calves.

[Wind howling] On Nelson Island, the resident bull is back in charge of his harem, but now they must face a far greater challenge.

After the freedom gained during the intense summer... the Yukon must again yield to the power of an Arctic winter.

The first snows already blanket the high country.

Cold is silently creeping back along the valleys.

This year's salmon runs may have been poor... but some fish have made it back to their spawning streams.

As life along the Yukon turns full-circle, this is where their journey will ultimately end.

[Grunts] [Grunts] Their deaths will help others to survive the winter.

And this is not the end of their story.

Nurtured by the Yukon's chill waters, salmon eggs pulse with life.

For the salmon and all those living in this wild country, the river holds the key to the future.

The Yukon will always be the natural and spiritual heart of this great wilderness... North America's legendary frozen river.

♪ "Rivers of Life", Season 2 is available on Amazon Prime Video ♪ ♪