Mackenzie River east into the Churchill River. The eastern portion of the Mackenzie basin is dominated by vast reaches of lake-studded boreal forest and includes many of the largest lakes in North America. By both volume and surface area, Great Bear Lake is the biggest in the watershed and third largest on the continent, with a surface area of and a volume of . Great Slave Lake is slightly smaller, with an area of and containing of water, although it is significantly deeper than Great Bear. The third major lake, Athabasca, is less than a third that size with an area of
Mackenzie River watershed drains about 20 percent of Canada. It is the largest river flowing into the Arctic from North America, and including its tributaries has a total length of , making it the thirteenth longest river system in the world. Through its many tributaries, the Mackenzie River basin covers portions of five Canadian provinces and territories – British Columbia (BC), Alberta, Saskatchewan, Yukon, and Northwest Territories. Thutade Lake, in the Northern Interior of BC, is the ultimate source of the Mackenzie River via the Finlay–Peace River system, which stretches through BC and Alberta. The Athabasca River originates further south, in Jasper