Dennis Drabelle, a former contributing editor of Book World, writes frequently about exploration.

In a sense, this book grew out of a mistake. Back in 1778, the great English explorer James Cook discovered a body of water — Cook Inlet, as it came to be known — in what is now Alaska. But he mistook the inlet for an outlet, as well as a portion of the Northwest Passage, a much-sought-after transportation corridor from Europe to Asia via the waterways of North America. (In its classic formulation, the passage was pictured as a sea lane, but a route through the North American interior might have served the purpose.)

Eleven years later, Alexander Mackenzie, a Scot representing a Montreal-based fur company, tried to confirm Cook’s theory by tying together the segments of the putative interior passage, starting on the St. Lawrence River, crossing lakes, following rivers, portaging where necessary and emerging at Cook Inlet, from which it was a straight shot to the Pacific Ocean. Mackenzie, too, had a body of water named after him: the 1,100-mile-long river canoed by him and his crew during the latter part of their journey. By the time Mackenzie arrived at river’s end, however, he knew he’d failed. Or, rather, geography had failed him. The stream, known locally as the Deh Cho, had swung north and emptied into the Beaufort Sea, an arm of the Arctic Ocean, which, being iced over most of the time, was not a reliable throughway. (For the record, at their closest, the Mackenzie/Deh Cho River and Cook Inlet are about 700 miles apart.)

If not for the mystique of the Northwest Passage, Mackenzie wouldn’t have made the trip, and the same probably goes for Brian Castner, a former U.S. Air Force officer who scratched a 21st-century itch to follow in Mackenzie’s wake. In “Disappointment River” Castner alternates an account of Mackenzie’s voyage with a chronicle of his own repeat in the summer of 2016.

In need of a second paddler, Castner lined up four friends, each of whom would take a turn, “like runners in a relay race, and pass me as the baton.” That’s a nice simile, but Castner is an uneven writer whose ultra-compressed sentences can leave the reader scratching his head: e.g., “It was a worn massif, indicative of an exhausted range that would succumb to the riverine thoroughfare [Mackenzie] transited.”

At his best, however, Castner has the Conradian ability to make you see and feel, as when he conjures up a summer-long plague with a few strokes: “The interior of our tent was . . . polka-dotted, brown on yellow, every surface covered with mosquito body parts and our own blood.” Or, even pithier, as he drives to his put-in point through a cloud of flies, “My windshield was a murder wall.”

“Disappointment River” abounds in vivid details. Transportation in Mackenzie’s time was so slow, Castner tells us, that it could take 3 1/2 years for a fur company to be paid for its wares. The mystery of how certain trees could have lost their crowns, and nothing else, to axe blows was cleared up when Mackenzie took a winter walk and found himself standing on a snowbank so high that “these towering stumps were at his knees.” While navigating a wide channel raked by winds, Castner’s co-paddler sometimes “hit air instead of water, and it looked like he was swatting at the waves to keep them at bay.” On the last, Arctic leg of the trip, “the sun warmed our backs, and we stripped down to our t-shirts, but [I] still wore long underwear and pants and wool socks and boots below, because my toes were still numb in the shade of the canoe even as my face and ears sunburned.”

Framing these interludes of astonishment, however, were days of sweatshop drudgery, with nowhere to pull over and make camp. “Of all the plagues of the Deh Cho,” Castner sums up, “the worst is emptiness.”

The emptiness may have hit him especially hard because he was always on the clock. His colleague-shuffling required multiple airplane flights, and as one rendezvous succeeded another, Castner had no time to leave the river corridor and do a little poking around. Nor did it help that some of the indigenous villages where he stopped for supplies were bogged down in alcoholism. The young people in these hamlets have few, if any, prospects for work, and teenage drunkenness there is often the prelude to a troubled adulthood.

In the last pages, Castner lets Mackenzie sum up his 1789 trip, whose outcome he faced with clear eyes. “Tho I was disappointed . . . [my expedition] proved without a doubt that there is not a North West passage below this latitude and I believe it will generally be allowed that no passage is practicable in a Higher Latitude, the Sea being eternally covered with ice.” Yet even negative results can be useful, and Mackenzie’s masterful effort earned him a knighthood.

It will also “generally be allowed” — though not by President Trump’s muzzled Environmental Protection Agency — that profligate burning of fossil fuels is changing the world’s climate. When Castner and his last paddling partner reached the Beaufort Sea, they found it ice-free. We finally have a Northwest Passage, but at what a cost!

Disappointment River

Finding and Losing the Northwest Passage

By Brian Castner

Doubleday. 334 pp. $28.95