The river is flowing backwards, back up from the sea.

They swim through silt, eyes wide, unblinking. Thirty, forty, fifty pounds of flesh, many thousands of them. Their backs speckled like frogspawn, the blush of their bellies, where the silver of their flanks fades into a deep and meaty rose. Jaws gawping, lips beginning to curve in upon themselves like pliers, propping their mouths ajar so that the river flows right through them, and yet for the rest of their lives these salmon will not eat, they will not drink. The organs that sustain them, the kidneys and the stomach, are shrinking as they sense the sweet water they have not known since they were smolts, finger big, years back. Familiar scents long forgotten are triggering changes in their brains and in their bodies: their chemistry has new priorities now. The ovaries of the female hen will swell to a sixth of her bodyweight during her swim upriver, the cock’s testes will increase fivefold.

For several years the salmon have roamed in schools throughout the Bering Sea, the chain of the Aleutians, the Sea of Okhotsk, ranging as far as the coasts of Japan. Their many species mingle. They travel further than science can reach, and much of what they eat and where they winter can only be surmised. The Yup’ik say that they live in human form beneath the waves, five houses, one for each tribe, and at the salmon king’s behest, each spring, they pull on their fins and silver skins and make for the human world. In the late Arctic spring, impelled before the others, the kings turn for North America’s west coast. California, Oregon, Washington, British Columbia, Alaska. They have iron in their brains, their compasses have led them here; now they scent their birthing pools. A chemical mix of vegetable and mineral unique to the waters of their birth that draws them on a thread up several thousand miles of river. They can distinguish a single drop from their home river amongst two million gallons of seawater.

The movement of one, changing direction, pulses through the rest, electric. At times they crest the surface, a dark sleek back, a dorsal fin, undulating like dolphins. These fish are many pounds of muscle, toned through years of swimming headlong into Pacific storms, and their flesh is red as blood. They force against the Yukon’s current, shouldering their way upriver, tacking crosswise through the flow, setting their fins like sails. Their shadows pass like clouds across the bottom. They rest in the eddies of boulders on the river’s bed, erratics left behind by glaciers. At the river’s mouth the water is still brackish, the current compounded with the flow of the tide. But it is diluting, and as they move further up the delta the sea slackens off its hold, resigning, letting them go. On this great in-breath of the land the kings spread up through the waters and their tributaries, permeating the watershed. Eventually, they will push thousands of miles into the continent’s interior. They will reach mountain lakes, they will reach the clouds.

It is the end of May, and spring is late. Which is not to say that it is a late spring, because this far north there is no such thing as a yardstick to measure the seasons up against (‘I’ve been here fifty years,’ in the words of one old-timer, ‘and the only normal year we had was two years ago’), but people say it is not where it ought to be. Mountains ring the town, and the snow still comes far down their peaks. The dandelions only opened last week. Bears have awoken from hibernation and, finding nothing to eat, have roamed within the Whitehorse city limits, sniffing out trashcans and chicken coops. The government has shot six in the past month.

Whitehorse, in the Yukon Territory, northwest Canada, is so named for the white manes that once tossed in the rapids of Miles Canyon, but that was more than a hundred years ago, back in Gold Rush times, almost prehistory; the dam went up in ’58 and the horses are all since drowned. Above the dam is a lake called Schwatka, after the man who mapped and did his best to tame the Yukon River on behalf of the US Army, and where Yukoners go to test drive their jet skis come the summertime. The floatplane base is little more than a jetty of planks buoyed up by oil drums, an old-fashioned balance to weigh in the bags, and a Cessna plane moored up on a thin rope, bright red against the blue. The pilot has only recently switched his skis over to floats. He cannot tell us whether McNeil Lake, where we are headed, will still be frozen over. I was in London three days ago and I am not used to uncertainty. But up here, out there, if someone hasn’t seen it then the information doesn’t exist.

Our bags come in at just below the permitted eight hundred pounds. The pilot asks our weights, so as best to arrange us in the plane. It is a perfect day, not a breath, and the mirrored clouds sit, precisely, upon the surface of the lake. Inside the cockpit it is sweltering. Take-off can be complicated when the surface is so glassy, no friction to catch against.

‘Going to be a fun one,’ grins the pilot, in cap and Ray Bans and check shirt, tucked-in, hauling up the bags, but before this he was out in Afghanistan and I assume that he lives for the fun ones. We strap ourselves in and put on the headsets and chug up to the inlet of the lake to maximize the length for take-off. He cuts the engine. We bob around. The lap of water, lolling against the floats.

I am travelling with Hector MacKenzie, a Scot who moved to Canada back when it was easy to move to Canada, as a young man in the late ’60s. He came and liked what he saw and stayed. He spent many years out in the bush, before moving into Whitehorse when his kids hit an age where they required more by way of schooling than a homestead could provide. Hector has climbed and guided and paddled all over the world. Now retired and in his seventies, his life is little different, except that he stays closer to home and canoes and skis only when the fancy takes him, which is often. A trim beard, white hair, a face that has stared down much weather. He exudes calm, which I welcome: up until now, I have spent perhaps a week in a canoe, on British rivers that look, to Canadian eyes, like trickles – the Medway, the Dart, the Wye. I have learnt my paddle strokes from books.

‘We’re just getting a bit of a northwesterly now, giving you a south-north departure,’ says the radio.

‘That’s us,’ the pilot says.

He starts the motor, and eases up the throttle. We begin to plane across the lake’s flat surface, spray flying from the floats. He fiddles dials and plugs something into the navigational display. We race past a couple of fishermen, out in a boat with rod and reel, their hands raised. The end of the lake, where the dam begins, is rapidly approaching.

‘Some pilots try and take off right away,’ he says over the intercom. ‘You can’t pretend you’re flying. You just treat her like a speedboat and she’ll come up.’ He nods. ‘You feel the heels come up there?’

I look back through the windows and and there is no longer spray. The pilot pulls back hard, and we rise up above the dam and up into the sky.

We climb. I look north, and already I cannot make out Hector’s house on the outskirts of the city. Whitehorse is a one-horse town, capital of the Yukon Territory, population twenty-five thousand. There are only thirty-five thousand people in the territory. People are fond of saying that there are more moose than people in the Yukon Territory, but in reality there are more of most things: more beaver, more salmon, more square miles. The red rust stain of a molybdenum mine grazes one slope, but for the rest it is valleys and forests of spruce, and the occasional trail cut through them.

Whitehorse’s first boom came in the last decade of the nineteenth century with the construction of the railroad, a link from coast to city, from where a sternwheeler to Dawson City made for a safe, if expensive, route to the Klondike goldfields. The second boom came with the construction of the Alaska Highway in 1942, two lanes that connected Alaska to Whitehorse, at the Canadian border, and from there to Vancouver and to the rest of the world. The population doubled, a third of the residents were squatters, the average age was about right to buy a beer. An old lady in town told me that when she first took her young kids south to Vancouver they cried because they had never seen anybody with wrinkles. There are many who came that never left.

We fly for an hour, heading east. Below, our shadow trails us. The lakes are as big as inland seas. Those in shade at the basins of summits are still frozen or still thawing, blue and white, like marbled paper. But up ahead Moss Lake is open, and that is a good sign, being as it is only a hundred metres lower than McNeil Lake, where we are headed. We cross rivers that run thin and white in sunlight. We pass Mount Hogg, Mount Placid, the mountains of the Big Salmon Range, and all the peaks that have never been named. We see no animals.

‘Do you come up this way much?’ I ask the pilot through the headset.

‘Summertime I bring up hunters,’ he replies.

‘Moose?’

He nods. ‘Moose, sheep, goat, bear. Anything that walks people will shoot it.’ He asks me what I am doing up here. I tell him I am looking for king salmon.

There are five species of Pacific salmon in North America: the chum, the coho, the sockeye, the pink, and the Chinook. Each has its own diminutive: the chum is the dog, or the keta, the coho the silver, the sockeye the red, the pink the humpy, and the Chinook is the king. The original Chinook are people of the Pacific Northwest, and their language formed the core of Chinook Jargon, a pidgin trading language that stretched from Alaska to the Columbia River, along what now forms the border of Washington and Oregon, and incorporated the words of many tribes, as well as French and English. Any Canadian will still say Chinook for king, the best and biggest of the fish that the Chinook people traded.

The Pacific salmon (Oncorhynchus, Greek for hook nose) and the Atlantic salmon (Salmo salar) share a common ancestor. They diverged between twenty and fifteen million years ago, during the Miocene cooling of the Arctic Ocean, which put between them a barrier of water too cold to cross. Separated, they became two distinct genera, but unlike the Atlantic salmon, which did not split further, the Pacific salmon went on diverging, resulting in the several distinct species of today (via some other remarkable examples: Smilodonichthys rastrosus, the sabre-toothed salmon, 10 feet long and 350 pounds). Each of these species has found its niche in the lakes, estuaries and mountain creeks of North America’s west coast. It is widely believed that Oncorhynchus was shaped by the dramatic geological changes along this coast, compared to the more stable east: huge uplifts along the Pacific Rim that produced the Sierras, the Rockies, the Alaska Range, all crushed into the sky, creating the varied habitats that allowed for the evolution of five species. And these species mutated further, each individual population adapting to the spawning ground it occupied, resulting in populations as genetically diverse as the number of spawning streams. Restless, migratory, wide-ranging across the oceans, they have returned in successive generations to the exact same streams where they were birthed, mother followed by daughter, father followed by son, for many tens of thousands of years. Pilgrimages are thought to have begun with nomads going back to the graves of their ancestors. Such is the salmon’s return.

The history of the salmon is the history of this land. Rock carvings in Alaska at the mouths of salmon streams are ten thousand years old. Big salmon etched into sandstone. Small salmon swimming upstream. A two-headed salmon, which suggests an awareness of their life cycle, of their departure and return. Carved by shamans, perhaps, to invoke the salmon’s annual pilgrimage; or insignia to mark the fishing rights to different salmon streams; or doodles, drawn on the slow days when the runs didn’t show or the river was in spate. Once people here would have had nets made from the sinews of rabbits and babiche, fish traps as funnels of woven willow. Dip nets made from willow bark, and spears tipped with bone. Chum salmon bones found in middens in the Tanana River Valley have been dated back eleven and a half thousand years.

The Yukon River is the longest salmon run in the world. Where exactly the Yukon has its source will never be resolved because there is no single answer, with countless tributaries rising across western Canada. There are 110 known rivers where the king spawns in the Yukon Territory alone, but the McNeil, where we are headed, is the furthest of those that the kings are known to reach. No species goes further, which is to say, the few kings that make it back to McNeil Lake have travelled further up a river than any other salmon on the planet.

These kings arrive at the Yukon’s mouth from somewhere deep in the Pacific, and they swim upriver, against the current, on a path that bisects Alaska, crossing the border into Canada’s Yukon Territory, taking a left up the Teslin River, crossing Teslin Lake, entering the Nisutlin River at the inlet to Nisutlin Bay, swimming through Moss Lake, and then up the McNeil River to its source. From the plane we can see some of that map, as far off as the Teslin, eighty miles away. The McNeil River is beneath us now, meandering across its floodplain, and as we crest the far end of its valley we see the lake and it is turquoise, sparkling, as though the several feet of ice that cover it for half the year were no more than a dream.

‘Nice spot,’ the pilot says. We fly up the lake’s eastern shore and bank and touch down on the water.

The ridge at the northern end of McNeil Lake, the St Cyr Range, its broad summits piebald with snow, is the traditional dividing line between the Tlingit and the Dene people, between the coastal and the inland, between the watersheds of the Yukon and the MacKenzie, and it is where the kings come to a stop. They are capable of herculean feats, but are unable to haul themselves on their fins over the crest of the ridge and gush down the other side. The ones that make it to the lake have climbed 1,054 metres into the mountains, and have swum against the river’s current for 1,990 miles. Just this week, on the daily email briefing from Alaska’s Department of Fish and Game (ADF&G), I read that the first of the year’s kings have been seen at the Yukon’s mouth, coming up through the tides. One or two of them will be bound for here, by forces as undeniable as gravity. By the time they arrive, at the beginning of September, I am planning to be down at the mouth. Somewhere along the way, our paths will surely cross.

The pilot leaves Hector and me on a gravel shore. It is cold, and the clouds are rolling in. We watch as the plane rises back into the sky, our hands raised high, and turns back towards Whitehorse. Then there is silence. We have a mound of stuff with us. Fishing rods and pots and pans and chairs and dry suits and clothes and medicines and ropes and a deflated raft and ratchets and paddles and spare paddles and four weeks’ worth of food, or thereabouts, and an enormous canvas tent. We are beside an empty trapper’s cabin, ply-nailed across the windows to keep away the bears. Rusted traps hang on pegs outside. It is the only sign of human life for perhaps a hundred miles. A shallow creek, with a stony bed, meets the lake here. A couple of sandpipers on stubby wings skim the surface of the stream. Their trilling whistle, which I hear for the first time, will become the melody of the river.

We camp a few hundred metres down the shore, away from the cabin, beside the outlet of the lake where the current starts to gather. It is getting late, and colder, but it will not be dark until, well, August, and we are not in any rush. Hector sets the tent and I gather wood, a mix of drift from along the shore and resinous dead branches pulled from the bases of the spruce trees. We cook a supper of rice and vegetables, and make a start on the meat that will not keep long. We have some whiskey that we can eke out for a few weeks if we are careful. After we eat, I sit outside the tent beside the fire. The channel is narrow enough that you could throw a rock to the far bank. The water draws your eye, far more than any fire does; it would feel odd to have one’s back to it. Passing, passing, already urgent for the sea. It will be there long before I am. You stare for long enough, and when you raise your eyes it is the land that seems to move.

It is as though we have gone back in time, back in season, to just after winter broke. There is scarcely new growth here. The catkins of the willows are tightly furled, and besides the willow there are no trees but spruce this close to the tree line. Sheets of ice bob in the sloughs, the side channels that branch out from the river. Only one species of flower, speckling the beaches, a sort of anemone, five white petals and a blue tinge underneath, like fine weather seen through clouds.

Three days, I think, from the centre of London. That’s all it takes.

I wake with a start; I must have overslept. Light streams in through the tent. I grab my watch. One a.m. I stare at it, uncomprehending. I fall back to sleep again.

I first came to the North in 2013. I came, ostensibly, to follow stories of climate change and oil, but really I came because I was lured in by the myth. I had grown up on Jack London and Farley Mowat; I had fleshed it out with Jon Krakauer’s Into the Wild and bluegrass and wildlife documentaries. I spent three months visiting every corner that I could: the site of the Exxon Valdez oil spill, twenty-five years on; a whaling festival in the Inuit village of Point Hope, the oldest settled site in North America; Newtok, slipping away into the sea as the permafrost beneath it thawed; Chicken, where gold miners from across the state came to celebrate the Fourth of July. I had read about a man called Mike Williams, chief of the Yupiit nation, who had spoken widely about the climatic changes that his people were experiencing. He invited me to his village, way out on the Yukon-Kuskokwim Delta. All flights to the delta pass through Bethel, and it so happened that whilst I was in town Mike was coordinating the trial of twenty-three Yup’ik fishermen who were in court for catching king salmon during a fishing closure in the summer of 2012.

‘Gandhi had his salt, we have our salmon,’ Mike said.

The closure had been implemented by ADF&G as king salmon numbers plummeted, unexpectedly and inexplicably. The fishermen pleaded not guilty. They were justified in fishing, so they said, because the taking of king salmon was part of their spiritual practice, their cultural heritage.

It was not big news; it made the local radio. But on the delta it was significant. There were tears in the courtroom. I wrote an article, which ran in The Atlantic. Back at home, I kept an eye on events. In 2014 a ban on all fishing for king salmon, commercial and subsistence, was enacted along the entire Yukon River, Alaskan and Canadian, an unprecedented move. In 2015 it was kept in place, albeit with some minimal harvest on the Canadian side of the border. In Canada the self-governing First Nations determine their own fishing quotas, with the national government only permitted to step in if a situation becomes critical; in the United States regulations are determined by the state departments of Fish and Game. Since the blanket bans of 2014 and 2015, ADF&G have been attempting to let people get some fish for themselves, whilst remaining conservation minded. That approach is in marked contrast to the years before the crash in salmon numbers, when the department was accused, from many sides, of driving the run into the ground through a lack of regulation.

No one is pretending that managing salmon is simple. Fred Andersen, a former fisheries biologist, has called the Yukon probably the most complex salmon fishery in the world. There are three thousand acronyms in play. Fisheries managers are attempting to regulate for a subsistence fishery, a commercial fishery, and a healthy ecosystem. During the fishing season, ADF&G will speak every single morning to discuss the strategy for the day. Stephanie Quinn-Davidson, who managed the Chinook run until 2015, told me that 85 per cent of her job was communication, with other managers, with media and, most crucially, with fishermen. The kings pass through a mosaic of state and federal land, and through the United States and Canada, each country with different divisions to its fisheries. Subsistence fishing is treated differently under state and federal law. Diplomacy between the United States and Canada is a further complication: the Yukon River Salmon Agreement, hammered out over thirty years, requires that fishing in Alaska be restricted to a point whereby between 42,500 and 55,000 kings be let across the border into Canada each year. This is a target that the US has failed to deliver five times in the past ten years, most recently in 2013.

In Alaska the runs of certain salmon species – the pink, the sockeye, the chum - still hit the millions on some rivers. Those on the outside forced up onto the banks. The backs of the ones above burnt by the sun, so they say, the bellies of the ones beneath scoured by the gravel, so thickly are they crowded. It is iconic, the ultimate symbol of the wild, the fishing trip to die for. Across the world, from the Far East to Europe, from North America’s east coast to its west, rivers that once knew a similar abundance see a fraction of their historic numbers; many have lost their salmon altogether. The River Salm, in Germany, after which the salmon is thought to be named, has no salmon any more. At one time Alaska was nothing exceptional. Now it’s simply all that’s left.

Yet in everything I read no one seemed able to agree whether the declines had come from poor management, long-term climatic changes, bycatch in the oceans, disease, or natural fluctuations. What seemed certain was that not only did the future of the king hang in the balance on the Yukon, this was the last chance on earth to get it right. The king is Alaska’s state fish, and across a border that the salmon do not recognize, in Western Canada, the bond to the Chinook is the same. If I was to try and better understand the North, I thought, then perhaps I should go looking for one of its most iconic species, the royalty of the river, before it was gone for good.

The Chinook has threaded together the communities that live along the Yukon for millennia. It intimately connected the lives of a Tlingit Indian at the river’s source and a Yupik Eskimo on Alaska’s coast, two thousand miles away, long before these people were aware of each other’s existence. It is a link to peoples’ ancestors and their hope for their children’s children. Many of the Yukon River’s villages, once the sites of seasonal fish camps, remain hundreds of miles from the closest road, and unless going by plane there is no way in but for the river. Travelling by boat at the same time as the king run and covering the same path as the fish, albeit paddling in the opposite direction, I hoped to better understand what is changing, not just in the life of the river, but in the lives of the people that depend on it. And I wanted to see how one of the most remote regions on the planet is experiencing the climatic and economic forces that are shaping the rest of our world. I had made long, slow journeys across countries before, and had found this way of travelling revealing in the interactions that it opened up and the stories that people shared, the trust that people placed in me because I had come from a village that they knew, was heading somewhere they had been. Now I wondered whether such a journey could also shed light on what was happening to the Yukon’s kings.

At half past six I wake once more. I am still jet lagged, yet to catch up with myself, and cannot fathom all this light. The river has been muttering all night. I step from the tent, and a pair of harlequin ducks, their faces painted, burst from the shore and fly, complaining, off down the meanders of the river. There is a skin of frost on all the gear. I make a small fire and brew some coffee in the little blackened kettle that has been everywhere with me. Mist hangs in the branches of the spruce on the far bank, and the air is chill and damp. I wear a coat and hat and gloves, but it is a chill that goes right through them. I put a pot of porridge on the embers, and watch as it bubbles.

The sand holds the stories of the night. The hoof prints of a moose and calf, like two series of quotation marks, emerging from the water and making off into the willows. The little nervous arrows of the sandpiper, pointing every which way, all along the shore. These female sandpipers are polyandrous: each male that she mates with she will leave to incubate her eggs whilst she goes off searching for another. Hector tells me this as we eat. Hector loves birds; he speaks of them as though they were his own prodigious children. Later, as we lie in the tent one night, listening to the whistle of some bird, he will suddenly, urgently, whisper:

‘Hear that? The semi-palmated plover. It is a sound that thrills me to my very marrow.’

I stand to do the dishes. There is an eddy here, on the outside bend, where the river begins in earnest. The water is slack and slowly turning, contrary to the flow, a deep pool slowly carved. I am scrubbing porridge from out the pot when I see the dart of little fish emerging from the shadows, pecking at the oats. And I gasp because it was as easy as that to find them. They are exactly where they were supposed to be. These are king salmon, a few months old, the first I have ever seen. I watch them as they feed on our breakfast.

At this stage, in the complicated lexicon of a fish that has spawned its own glossary, they are called parr. It is the point where the parr marks appear, the oblong splotches that run the length of them like inky fingerprints and, like fingerprints, distinguish one species from another. The marks are obscured as they age, but for now they are camouflage against the gulls and terns and pike and mergansers and otters and sheefish and loons and everything else that hunts them. They hold their position against the current, their narrow bodies pulsing, their tiny fins making constant, incremental adjustment, feeling out the river’s flow. Each is perhaps one inch long. One shoots for a bug caught on the surface, shakes it, and slips back inside the group. They stand out against pieces of sunken drift; against the murk of the bottom they are almost lost. When I get down low and peer through the reflections I count maybe twenty or thirty. They will have been born, not quite here, but close to here.

Where to begin a story as cyclic as the salmon’s? Had you been here in the autumn, in October, when the last of the leaves hang from the willow and the snows come any day, before the rivers are entombed, you would have seen little sign of them. But if you knew where to look, perhaps in that creek that came in by the trapper’s cabin, there would have been patches of paler, upturned stones in the beds amongst the summer’s growth of algae, maybe ten feet long by half as wide. These places are the redds (a Celtic word, ‘to tidy up’), the Chinooks’ spawning grounds. They were excavated by the female kings that reached here at the end of summer, lying on their flanks against the riverbed and shovelling with their tails, carving trenches well over a foot deep. Here they deposited their eggs, and the males that fight for space beside them ejaculated their milt, sometimes several males at once. Held together by their stickiness and the back eddy of the depression, the egg and seed fertilized.

As they start to develop, the eggs toughen and darken. The female works her tail again and begins to bury them, flicking gravel up into the current so that it falls across the bed. They settle into spaces deep amongst the stones. And as winter comes on, and the creek freezes over, the eggs begin to change. The speed of their development is directly governed by the temperature of the water. Within a few weeks two black specks peer out from the inside of each. Beneath the ice the current flows, scouring the rocks of silt and the wastes of growth and allowing the embryos to breathe. The temperature drops. At minus forty nothing moves except the raven. The air is so cold it cracks; too cold for it to snow. The smoke from the trapper’s cabin rises straight up like a taut string. In midwinter, the salmon hatch. Huge goggle eyes on tiny heads, a translucent body with the line of their spine discernible inside, and the yolk-sac beneath their chin, like a goitre, attached by a single vein like the root of some bloody plant. Known as alevins now, they wedge themselves deep amongst the stones, turned by their instincts to face upstream so that the water flows across their nascent gills. The stars revolve; the sun grazes the horizon for an hour each day; the northern lights rush across the sky. The weeks pass and the yolk diminishes, and the alevins work their way up, day by day, through the gravel of the redd. Already they are imprinting the particular scent of this creek, the scent that they will use for their map home years hence. By the time they emerge from the creek-bed, over half will have already perished.

They hold there, in the tiny eddies of the stones of the bed, digesting what flows through their mouths, whatever microscopic organisms. They are fry. Each of their fins – dorsal, adipose, tail, anal, pelvic and pectoral – is identifiable now. They swim, they feed, on flagellates and rotifers and on tiny crustaceans, microscopic organisms as intricate as snowflakes. The days are warming; during the sunny hours the snows are melting. The ice above begins to crack, and one day, in a rush, it all goes out. A few will begin their journeys downstream now, but the majority remain for a year in these pools. The sun is high in the sky overhead and it comes unfiltered to the bed. As they grow they eat larvae and nymphs and other life that swirl about the water. They are silver beneath and speckled and olive on top and they are touched with the marks of the parr. And here we find them, this first morning, two thousand miles from the sea. The omen feels a good one.

We inflate the raft, and load the gear. Hector has chosen a raft for this first week because of the whitewater on the upper Nisutlin River. We have been unable to find much detail on the severity of the rapids except for Arthur Saint Cyr’s map of 1897, commissioned by the Canadian government as part of a survey of ‘all-Canadian’ routes to the Klondike goldfields, on which Cyr has marked ‘six miles of bad rapids’ through the length of Nisutlin Gorge. A fish biologist who knows the area has advised us that they are rated Grade 6, which does not exist, is off the chart, almost biblical, and I can only hope that he has got confused with the number of miles. But that is still some days away. We paddle out into the current.

We are flowing markedly downhill, and the water, though flat, is swift; it would need a quick jog to keep up. The spruce here are vast. In this climate, at this altitude, their growth is glacial: some of the largest will be centuries old. It can be hard now to find decent-sized logs for cabins, all cut down years ago, but these would be ideal if you were so inclined to set up home here. Where they have fallen at the river’s edge they lean out over the water, grasping; sweepers, they are called. The river moves fastest on its outer curve and often we are led straight to them; on the tight corners they are tricky to predict. Within ten minutes we have gone straight through one, and I have lost my hat. The raft is a pile of dead needles. In places these logs have detached, and run aground mid-river. Other logs jam on them, and then soil and silt build up behind. Eventually the willows take root, knitting the earth together, and islands form, islands we must dodge around.

By lunchtime the river has opened into Moss Lake, and the current fades away. A pair of Arctic terns, who see more light than any other creature on earth, hover, cruciform, far out above the water, scanning for young salmon. These terns have travelled the length of the planet to nest here, and in a few months they will fly back to the Antarctic. They have peaked caps pulled down low over their eyes; it gives them a debonair swagger. The sun glances off the water and there is no shade out here; I feel dizzy and sick with heat. We listen to the slosh of the paddle strokes. Ellipses and ovals and circles shimmer over the lake’s still surface. Then in some hours we come to the end of the lake, and the current has us again.

With every few hours that we descend the river we race away from winter. There are spruce tips on the spruce now, a luminescent green against the dark of last year’s growth. Spruce tips are sharp and lemony, almost like capers in a stew. A few hours more and the catkins on the willow are beginning to unfurl. We see the first aspen, and then later the first cottonwood, their new leaves so young and bright it is as though they have been varnished. And new flowers, shooting star, lupin, vetch, flecks of colour amongst the greens and browns, and then the first shoots of the fireweed, which Hector picks and adds to salads. We make camps on small islands and sandy beaches, and with the light there is little meaning between one day and the next, each are just pauses in the journey.

Three days from the lake, the McNeil pours into the Nisutlin through a canyon of rock, anticlines bent into its faces. The river takes the name of the Nisutlin now, a deference to the name of the Tlingit people, whose land this is, although the McNeil is much bigger than this tributary. Rounding a corner one afternoon we come upon a moose, standing alone on a gravel bar, sopping. It stiffens and sniffs the air when it sees us, but remains where it is, its stare fixed on us. There is a high-keyed hum of alertness. It is shocking, suddenly to stumble across another mammal out here. We stop paddling and float, the better not to scare it, watching it as we drift around the bar. Then all of a sudden Hector points and says ‘Osprey!’, and there it is, taking off from the top branches of a spruce with a fish held between its feet, and the moose bolts for the woods, picking its legs high like some huge improbable puppet, and it is all there in my field of vision, moose, osprey, fish, river, and it could be this time or it could be any other.

On the fourth day we come to the rapids. I had a sense of foreboding in camp as we rigged the raft that morning, strapping down the gear, attaching throw bags and flip lines, discussing eventualities: what to do if one of us falls out, what to do if both of us fall out, how we’d go about finding each other, what to do if we lost the boat. It is a long, long walk to Whitehorse. We have little idea what to expect. And then, for an hour or two we drift, along pleasant meanders, through sun-baked forests. We see goldeneye and canvasback, pintail and widgeon. Mountains recede in deepening shades. And I am almost lulled into forgetting what’s approaching when we turn a bend and see ahead of us a line of rippling white, stretching from bank to bank.

‘That’s us,’ says Hector, with a twinkle.

And we fall into them.

The mutter of the river becomes an all-consuming roar. The waves rise up, malevolent, great troughs and burbling peaks. The raft bucks over them, and we dig the paddles deep and try to hold her straight. Behind rocks that have tumbled from distant mountainsides are gaping holes that would flip the raft like a penny. The river wants to take the boat in there, and we strain to keep her out.

‘Back up,’ says Hector, unfalteringly calm. ‘Sweep hard. Harder. Now.’

We swing sideways in a trench of water and the river sloshes over us, and shamefully I dive for the deck. The water barrels over me. The river heaves and flexes beneath my hands. The raft pivots where Hector jams the paddle in. And then we pop from the end of the rapid, soaked, unscathed, and I get back in my seat.

‘That was meant to be the easy one,’ he says, smiling, as though to say, well, we’re committed now.

They blur one into another. We climb and plunge, the waves breaking in our faces, wiping the water away to see and bending back into the stroke. The river lunging, shaking, clawing at the raft.

‘Well, look at that,’ says Hector, pointing at ducks as we shoot over a wave. ‘Another pair of harlequin. How fascinating.’

I think that I am scared, but each time we emerge from the end of a rapid I find myself yearning for more. And there are more. They are continuous. We pick a line down the left bank, trying to dodge the worst of it, but the flow pushes us out into the middle channel, and we ride it, finding ourselves in an eddy on a sharp bend, the current pushing us one way, but not enough for us to miss the mound of rock that is now looming at the top of the next falls. I hear the edge in Hector’s voice as we heave to try and pull right, and we do, grazing past the rock, gazing into the hole that yawns beyond it, and I’m looking behind, and Hector’s shouting ‘Back! Back!’, and I realize we’re rowing backwards past this next one, and we make it, just, turn to right ourselves, and on it goes. And all I can keep thinking is, the salmon swim up this.

And then, in a moment, it is over. The river broadens, slows, the land seems to flatten out. The sand bed sucks the current from the water. We lie back and float, and let the sun dry us off. I look across at Hector. We’re both grinning, with adrenalin, with relief.

‘I used to scare myself about once a week,’ he says. ‘Now I try and keep it to once a year. I hope that that was it.’

Some days later the Nisutlin meets the South Canol Road, the river’s first scrape with civilization. Hector is to leave me here. He must return the raft, and Ann, a friend of Hector’s who comes to pick him up, has brought me my canoe. There is just one small rapid left between here and the ocean, 1,926 miles away. The canoe is bright yellow, fibreglass, eighteen feet long, which is a big one, but for the many weeks of food I will have to carry further on down the river, when all roads and stores run out, that space will be essential. For now, it is a welcome change. There has been a fierce headwind, and rafts are not designed for that. The canoe holds its line better, it will be less of a slog. I can hear the car driving away for a long time before I am left there in the silence.

For four days I paddle down the slowing and widening Nisutlin. The sun is hot, the scent of warm spruce on the wind, and the landscape feels benevolent. I pass high-cut banks where the land has been bisected. Fifty, a hundred feet high, precipitous, topped with a line of spruce, the earth’s inner workings exposed. There are trees which have slipped from the top and slid, and protrude now across the water. The hollows of bank swallows, Riparia riparia, pepper the exposed sand, neighbourly as blocks of flats, as though the cut bank had been used for target practice. Gusts of birds surround the boat, darting and dipping and chattering to the water. There are scarcely any insects yet, another symptom of the late spring, and I wonder what these birds will feed on, arriving at the end of epic journeys, or whether they have anything to feed on at all. A pair of mergansers in flight, necks flung out and quacking, hurry past me up the river.

It comes almost as a surprise to remember how alone I am. The Yukon watershed has a population of a quarter of a person per square mile for a third of a million square miles, the equivalent to a pre-agrarian society. If the planet were similarly populated the global population would be that of Istanbul, which is what it was seven thousand years ago. Out here, any evidence of human existence feels like an artefact, signs of other beings distant not through history but space. A tent peg, a shotgun shell, a penny: each object requires careful consideration, as much as a spoor print or a gnawed stick might. Once, on a bar where I have pitched for the night, foraging for wood, I come across the embers of another, older fire, scattered now to charcoal, and immediately I start, look up, as though aware, all of a sudden, that I am not the only inhabitant of this landscape.

One evening I stop to make a fire for coffee. It is ten o’clock and the sun is level with my eyes. Directly opposite a smudge of moon, like a thumbprint on the sky. There is a creek falling down between some banks, and I fill the kettle there and put it on the few sticks that are burning. I stand, stretching my shoulders out, waiting for the boil. The smoke of the fire rises thinly. There is a rustle of leaves up the bank. I start, jumpy for bears, and there is a fox high-stepping down the slope, through the tangle of fallen aspen. He hasn’t seen me yet. He has an altogether different poise from the London foxes that I know, his coat glossy and thick, his tail bushy and high, like a rooster. He is several shades of red and rust and brown in different patches. He pauses, one forefoot raised, and drops his head, and then, assured that everything is as it should be, he carries on down the hill.

I lose sight of him somewhere in the scrub. I pour the coffee, piss on the fire, and get back in the boat, intending to drink as I float. Coffee to go, I say to myself, and laugh at my own joke, with no one around to tell me otherwise. I untie the bowline, and drift slowly along the bank, facing back the other way that I have come. The fox is there again, a little further down the bank. I fix the binoculars on him. He has a patch of white on each cheek, and he is looking right at me. I lower the binoculars, and look right back at him. I keep on drifting, backwards, gradually away. He keeps on watching, attention held. There is no rush. And he bends, and sticks his neck out, drinks, takes a final look at my diminishing form, and then he dances to the top of a log across the creek and carries on with the evening.

In a week I come to Teslin. The first village on the river, it sits on the west bank where Nisutlin Bay meets Teslin Lake, where the Alaska Highway crosses the water on a long bridge of steel girders. It is a three-hour drive from Whitehorse, but I have gone the long way round. Telin-to, the thin long lake. About 450 people live here, the majority Tlingit First Nation. I moor up at the foot of a slope and climb it to the Yukon Motel Restaurant. I order coffee and cherry pie. There are a lot of people, all of a sudden. There is British politics on the television. I am here to see Richard Dewhurst, a meeting organized long before I had got on the river. Teslin is the closest village to the headwaters of the Yukon, and so, as Richard tells me, ‘we’re the last people on the planet to utilize that fish’, by which he means the Chinook. In his fifties, he is Game Guardian with the Land and Resources department of the Teslin Tlingit Council. He asks me if I would like to see his mum’s old fish camp.

Richard drives a RAM 3500 Heavy Duty Cummins, all waist-high tyres and suspension and chrome. He is a large man but he looks small within it. He wants to know if I saw many moose on my way down the Nisutlin. I tell him I did, a lot.

‘Bulls?’ he asks.

I nod.

‘Big ones? Big like that?’

He stretches his arms wide to demonstrate the size of rack, so wide that he almost spans the vehicle, and he smiles at the prospect. We bounce down a road off of the highway, a dirt track, really, overgrown with stems of alder. The Alaska Highway came through in 1942, part of the war effort, in case the Japanese turned up via Alaska. Teslin went, in a matter of weeks, from a remote bush village to an overnight drive to Vancouver. Elders remember bulldozers cresting the horizon and forging a path towards their village.

We come to a stop at the top of the beach on the lake, a few miles from the village, get out and slam the doors shut. In the silence, the water pushes softly against the pebbles of the shore. A ground squirrel runs along a pole of the collapsing fish camp, chattering at our disturbance. Once his family would have rowed up here. Richard walks through last year’s leaves, running his hand over things. A couch with the foam poking out of it, the fake leather peeling back like a half-skinned animal. Floats strung up in the trees, a fallen flue, battered tubs for washing fish. The fallen corrugate of one structure has been placed sidewise around its wood supports, forming a windbreak three feet high, and two plastic chairs are set within it before a fire pit. Richard stares at it.

‘That’s new,’ he says, after a time.

He rolls a cigarette from the pouch that he takes from the top pocket of his denim jacket. It is so quiet that I can hear it burning, crackling like twigs. He perches on the edge of a table that would have been used for the cutting of fish, one eye clenched against the rising smoke, and he peers back at me. A thin scar runs the length of his nose. This was his mother’s fish camp, he says. They would come here in late July, when they saw the first wind on the water and the whitecaps further out, the whole family of siblings and cousins and nephews and nieces and friends, and they would stay here until late into August. Drying fish, smoking fish, picking berries, hunting moose. A place where the young could spend time with the old, where the kids heard stories, learnt to hunt, learnt to work as part of a team. The salmon blood brought in grayling, and the kids stood in the water with a line and a flashlight and a hook baited with salmon eggs and caught their first fish for themselves.

‘They learnt how to run motors,’ Richard says. ‘And they learnt that water, eh. That water could take your life or it could save your life. You got to have respect for it. I do, anyways.’

He shows me photographs he has brought with him, tinted with age. Salmon laid out on the beach in a row, like a strike in ten-pin bowling. Himself, at camp, in his younger, trimmer days. His Dad, in brown shirt and Stetson, smoking a cigarette and squinting at the camera, holding up an absolutely enormous king, his mother grinning in the background. Another salmon, held up by his uncle.

‘My uncle’s got four or five inches on me,’ says Richard, ‘so you can see how big that fish is.’

The first salmon that they caught, they would welcome it, and thank it, for coming so far to feed them. They would roast it, guts and all, and everyone in camp would take a piece, and once there was nothing left but bones they would put the bones back in the water, pointing in the direction that the salmon had come, so that the next year they would bring more. When the salmon were running no one could swim. Back in the good old days they could put away eighty fish, enough to last the family through the winter. But that was the good old days. There was a time when Teslin was a ghost town during the summer, with everyone out at camp. He shakes his head, remembering.

‘My mother’s of an age now where she’ll never see fishing here again,’ he says.

Richard built the cutting room twenty-one years ago, and he got one year’s use from it. The decline had started slowly, almost imperceptibly, although the elders had been warning them for decades that something was changing with their fish. Where Teslin is located, at the very endpoint of the run, they saw those changes first, both in the size and in the number of Chinook. To begin with they restricted their own fishing to five days of the week. Then it went down to three days. Then it was two. Nothing seemed to make a difference. Twenty years ago, all of the Teslin Tlingit Clans came together in an emergency meeting and they voted to shut it down entirely.

They agreed it was only temporary: just shut it down until things improved. But things had not improved. It has been tough, Richard says, to stand on the shore and see those salmon swimming past, tough when you know downriver in Alaska the people are still fishing. Tough when you watch those Alaskan TV shows and see them with their caches full of fish.

‘Is it worth it?’ I ask him.

‘There are some people who think, if they’re fishing, why are we trying so goddamn hard?’ Richard says, grinding his cigarette between two fingers. ‘But then you turn around and you look at your kid, and that gives you all the reason in the world.’

The salmon that comes to Teslin now is flown in from Atlin, another Tlingit village a hundred or so kilometres southwest, whose people catch their fish on the Taku River. Little of it is king, it is mostly sockeye and coho. It is expensive and it doesn’t taste the same, and much of it is so rich and oily that people’s bellies are not used to it. It dries differently from what they know, the ways passed down from their ancestors. And none of it comes with the heads on, which is the greatest delicacy of all. There are young people in the village who have never fished, who think that the drone of a bush plane from beyond Mount Bryde signals the start of the salmon run. Flying fish, they call it now.

Teslin did not fish for twenty years, but then, last year, they did. They made two fish camps, one on Teslin Lake, one down the Teslin River, and between them caught a little less than forty fish. Once they might have caught a thousand, but the idea was symbolic, ceremonial. There was a need to conserve the fish, but there was also a need to preserve the Tlingit culture. With those fish they cooked up a feast for the whole village.

‘First time we ever set net for the generations so they can see our salmon when it comes up here,’ Madeleine Jackson, one of Teslin’s elders, explains to me the following day in the tribal government offices of the Teslin Tlingit Council. ‘Man, we had five Clans here,’ she says. ‘I took one from each Clan to set that net, and when they came back next morning I took one from each Clan to run that net. So when they bring it out we had a ceremony and, man, there was tears of everybody, crying because first time they ever see that salmon. And some of those elders came and showed the kids what to do, how to cut fish, and how to respect it. It’s not for us we’re doing this. The elders had their share. I had my share. It’s for the younger generations coming behind us.’

‘The salmon are a giving people,’ says Madeleine’s nephew, Duane Aucoin, sitting beside her. ‘They find their existence in a lot of ways by giving us life. And they give their lives for their children, when they spawn, in how far they swim. Their only goal is we need to do this for our children. What a good example for people to follow.’

He pauses.

‘Now those Atlantic salmon,’ he says, ‘they’re different. They don’t die when they spawn. They swim out to the ocean and they tell their partners, see you again next year!’ He smiles at me. ‘That might be the European influence.’

In Richard’s camp, I asked him how he enjoyed the feast. He shakes his head.

‘I never went,’ he says. ‘I never participated. In my belief, there was one chance in a million that my son – he’s five years old now – would ever get to fish. And I would never fish again if I thought that he could experience what I’ve experienced in my life. It makes me feel like we’re cheating, that we’re not being honest with ourselves.’

We stand there, side by side, looking out across the water. In the distance, in the shallows, outside one of the summerhouses by the highway, some chubby kids splash about on inflatable kayaks. Their shouts drift across the water. It looks as though, almost by consensus, every spruce tree has released its pollen on this morning, and there is a tide of its yellow dust along the shore. This old camp has the feel of a graveyard, of a place that has known grieving, but a place now calm, at rest. I listen to Richard’s slow and heavy breathing.

‘It sure was nice to hear those waves,’ he says, ‘when you lay down to sleep at night.’