GREAT SLAVE LAKE (ATHAPuscow), a lake of Mac kenzie district, Canada. It is situated between bo° 5o' and 62° 55' N. and Io8° 4o' and I17° W., at an altitude of 391 ft. above the sea. It is 325 m. long, from 15 to 5o m. wide, and includes an area of 9,77o sq.m. The water is very clear and deep. Its coast line is irregular and deeply indented by large bays, and its north eastern shores are rugged and mountainous. The western shores are well wooded, chiefly with spruce, but the northern and eastern are dreary and barren. It is navigable from about the 1st of July to the end of October. The bulk of its water empties by the Mackenzie river into the Arctic Ocean. It was discovered in 1771 by Samuel Hearne.