The name in the Dene language originally referred only to the large delta formed by the confluence of the Athabasca River at the southwest corner of the lake. Prior to 1789, Sir Alexander Mackenzie explored the lake. In 1791, Philip Turnor, cartographer for the Hudson’s Bay Company, wrote in his journal, "low swampy ground on the South side with a few willows growing upon it, from which the Lake in general takes its name Athapison in the Southern Cree tongue which signifies open country such as lakes with willows and grass growing about them".