The water towered all around me. The standing waves were thatched and stacked up tight, each white-topped ridge squared to the next as in a log cabin quilt pattern. This is a slalom, I thought, but too late. My kayak broke through the first wave, I clumsily jerked 90 degrees, pinballed back, knocked into the next wave, and tried to turn, but my edge was hopelessly off, and when I hit the third, the water grabbed my low chine and I tumbled from my boat.

It was cold and dark and I was upside down and everything was loud in my ears. I pushed off, twisted, kicked, hit my head. As if I were a clapper in a bell, the ring of my helmet on my boat in the center of my brain. My hip hit a rock, hard, and then I pulled my feet up, so they couldn’t get trapped on the bottom, and I tried to swim. I was still moving with the current at speed, and I pulled the water and pushed my boat away and I broke the surface and took a breath. My paddle was still in my hand.

“Swim over here,” John called to me, calm as could be.

I did, and reached out for the handle dangling from the tail of his kayak.

“Do you want to ride this one out?” he asked me, only occasionally dipping his paddle in the water to maneuver us around rocks.

“I think that would be best,” I managed. A wave broke over my head, and I took a big long drink of the river.

Once on the granite shore, I cinched down the straps on my vest, tight as a tick, and remounted my kayak.

“Are you cold?” John asked. The sun blazed, but I was shaking from the shoulders down.

“No, I think it’s adrenaline,” I said.

“That was Sambuca,” he said, naming the rapid that owned me. “Wanna try Flipper?”

“The next rapid is called Flipper?”

I followed John’s line through a calm pool and to the head of the next whitewater plume. It rose before me in layers, and I felt small beneath it. I got through the first crest, the second, the third. I was through the wave train; I had made it. But then I hit the recirculating water at the bottom of the rapid, eddies on each side meeting as a boil. One eddy fence grabbed my nose, the other my tail, I felt my kayak spinning, and then I was in the cauldron again.

***

In the summer of 2016, I set out to retrace Alexander Mackenzie’s famous expedition to the Arctic Ocean. Mackenzie was a fur trader seeking the Northwest Passage, and in June 1789, with his Chipewyan partner Awgeenah, their hired voyageurs, and wives, he embarked with a little flotilla of canoes from Lake Athabasca, searching for the Pacific. Eventually, they’d paddle the river that now bears Mackenzie’s name, but the first river they descended was the Slave.

To understand that river as Mackenzie saw it, I contacted Leif Anderson and John Blyth, organizers of the Fort Smith Paddling Club, and asked them to take me out on the Slave. As a lover of whitewater, I knew the Slave’s reputation — incredible volume, world-class rapids — and the chance to kayak even a section would be like getting to play catch in Yankee Stadium.

There was no cell service on the way to Fort Smith. On my phone’s useless green blur of a map, the dirt road looked like a paper cut on a whale. Google Maps’ coverage of the Northwest Territories is primarily low-def, feeding the impression most southerners have of this rocky socket of Arctic wilderness: it’s big and it’s empty.

Big, yes. But empty, not quite. Fort Smith proved to be a densely built town of tidy houses and government offices, home to 2,500 people, roughly half indigenous. I arrived on the eve of Aboriginal Day. Smoke rose from the cookout at the fire circle, and volunteers set up white tents and teepees for the men to play Hand Games, the popular traditional Dene guessing game.

The Slave River is immense, as wide as five normal rivers, and crisscrossed with pour-overs and channels. It reminded me of the rapids above Niagara Falls, but many times wider. The Slave drains northern British Columbia, half of Alberta and upper Saskatchewan, and the rapids at Fort Smith are formed where a northern quadrant of the Canadian Shield meets the tar sands. Flocks of white pelicans, the northernmost breeding colony on the continent, perched on rocks or floated in eddies, serene among the boil.

Sand and granite, gulf coast seabirds amid black spruce, it was all juxtaposed and spectacular. My mind reeled at the view.

I eventually met up with Leif and John. Leif is a giant blond Viking with a raging mullet haircut. He’s also a member of the U.S. Freestyle Kayak team and travels all the way from Idaho every summer to train. John, in contrast, is small and dark, with good looks that I’d call all-American if he weren’t Canadian, born and bred in the North. In the videos I found of him online, John has long dreadlocks, but he had recently lopped them off; Leif picked on him for looking respectable. Like a ski-bum kid who doesn’t know his good fortune to grow up in Vail or Snowbird, John learned to kayak on the Slave and has no need to travel like Leif.