Mackenzie River Mackenzie River The Mackenzie River (Slavey language: Deh-Cho , "big river" or Inuvialuktun: Kuukpak , "great river"; ) is the longest river system in Canada, and has the second largest drainage basin of any North American river after the Mississippi River. The Mackenzie River flows through a vast, thinly populated region of forest and tundra entirely within the Canadian Northwest Territories, although its many tributaries reach into four other Canadian provinces and territories. The river's main stem is long, flowing north-northwest from Great Slave Lake into the Arctic Ocean, where it forms a large delta at its mouth. Its extensive
Lake Athabasca depth of , and holds of water, making it the largest and deepest lake in both Alberta and Saskatchewan, and the eighth largest in Canada. Water flows northward from the lake via the Slave River and Mackenzie River systems, eventually reaching the Arctic Ocean. Fort Chipewyan, one of the oldest European settlements in Alberta, is located on the western shore of the lake, where the Rivière des Rochers drains the lake and flows toward Slave River, beginning its northward journey along the eastern boundary of Wood Buffalo National Park. The eastern section of the lake narrows to a width of