Canada’s longest river system drains a fifth of the country north
With the Slave, Peace, and Finlay, the Mackenzie forms Canada’s longest river system and North America’s second-largest drainage after the Mississippi. The main stem alone runs 1,738 kilometres from Great Slave Lake to an Arctic Ocean delta.
Ultimate source water sits in Thutade Lake, British Columbia, before the Peace–Athabasca Delta and Slave River feed Great Slave Lake. The Peace and Athabasca meet in a vast inland delta at the west end of Lake Athabasca, and the Slave then runs 415 kilometres due north. Tributaries touch five provinces and territories; the watershed covers about twenty percent of Canada. Slavey speakers say Deh-Cho, “big river”; Inuvialuktun uses Kuukpak, “great river.”
The main stem leaves the west end of Great Slave Lake about 150 kilometres south-west of Yellowknife. Near Fort Providence the channel narrows to about 800 metres after leaving the lake several kilometres wide. At Fort Simpson it takes in the Liard, its largest direct tributary, then turns north past the North Nahanni between the Mackenzie Mountains and the low hills of the Canadian Shield. It spreads to 6 or 7 kilometres across at Norman Wells, drops about 6 metres through the Sans Sault Rapids, and beyond Point Separation fans into a delta of channels and ponds covering more than 12,000 square kilometres.
The whole basin spans some 1,805,000 square kilometres, 54 percent of it upstream of Great Slave Lake, and permafrost underlies roughly three-quarters of it. The Continental Divide separates it from the Yukon and Fraser basins, and in the east it holds Great Bear Lake, the continent’s third largest.
Prehistoric migrations into North America may have used the valley more than 10,000 years ago. Inuvialuit, Gwich’in, and other Indigenous nations long lived along the corridor that later became a fur-trade highway. Norman Wells oil in the 1920s sparked limited industrialization in an otherwise thinly settled boreal–tundra expanse.
Source: Mackenzie River
