Athabasca, Lake, fourth largest lake of Canada, c.3,120 sq mi (8,100 sq km), c.200 mi (320 km) long and from 5 to 35 mi (8–56 km) wide, NE Alta., and SW Sask., at the edge of the Canadian Shield. A part of the Mackenzie River system, the lake receives the Athabasca River from the south and drains N into Great Slave Lake by way of the Slave River. Gold and uranium are found nearby. Fort Chipewyan was built (1788) at the west end of the lake by Roderick McKenzie of the North West Company and has been maintained. Steamers of the Hudson's Bay Company ply the lake in summer between Chipewyan and Fond du Lac, from where the canoe route runs by way of Wollaston and Reindeer lakes to the Churchill River. Philip Turnor, the British surveyor, surveyed and mapped the lake between 1790 and 1792.