Mackenzie River

River in the Northwest Territories, northwestern Canada; about 1,705 km/1,060 mi long (from the Great Slave Lake to the Beaufort Sea). It originates as the Athabasca River in British Columbia and flows over 966 km/600 mi to Lake Athabasca; it then flows northwest from the Great Slave Lake until it enters the Beaufort Sea (part of the Arctic Ocean). The Mackenzie River is navigable from June to October, when it eventually freezes over. It is the main channel of the Finlay-Peace-Mackenzie system (4,241 km/2,635 mi long), the second longest system in North America.

The river was named after the British explorer Sir Alexander Mackenzie, who first saw it in 1789. Its most important tributaries are the Liard, or Mountain River, Peel River, and Bear River. The basin is heavily forested, and little of it is settled, but there are mineral, gas, and oil reserves, especially in the delta region. Several small settlements are situated in the delta area: Fort McPherson, Aklavik, Unuvic, and Raindeer Depot.