Athabas'ca (locally La Biche, 'red-deer or elk river'), a river and lake in the North-west Territory of the Canadian Dominion, forming part of the great basin of the Mackenzie. The river rises in the Rocky Mountains, in a little lake at the foot of Mount Brown, one of the highest points in the range, and flows over 600 miles NE. and NW., until it unites with the Peace River, from beyond the Rocky Mountains, to form the Slave River, which, again, after passing through Great Slave Lake, takes the name of the Mackenzie (q.v.). Lake Athabasca receives nearly all its waters from, and has its sole outlet in, the Athabasca River, which traverses not its length but its breadth, and that not in its middle, but at its extremity. It is 230 miles long, and from 14 to 30 broad. It was discovered in 1771 by Samuel Hearne, and named by him Lake of the Hills. - Athabasca, formerly one of the four divisions of the Canadian North-west, defined in 1882, between British Columbia and a line to the east of the Athabasca River, and between the parallels 55° and 60° N. lat. In 1905 it was about equally divided between the newly formed provinces of Alberta and Saskatchewan.