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
Geikie River (Saskatchewan) Fond du Lac River which flows out of the lake to the north-west where it drains into Lake Athabasca which ultimately drains into the Arctic Ocean via the Mackenzie River system, or into the Cochrane River which flows out of the north-eastern side of the lake and into Reindeer Lake which drains via the Churchill River system into Hudson Bay. If Hudson Bay is defined as part of the Atlantic Ocean then the Geikie River is the largest river in the world that drains naturally into two oceans. The Geikie River is bridged by Highway 905 at the highway's 184