Dease Lake is a lake in the Stikine Plateau of the Northern Interior of British Columbia, Canada, located at the head of the Dease River, which flows north then northeast from the lake to join the Liard River. The community of Dease Lake, British Columbia, formerly Dease Lake Post, is located at the south end of the lake, straddling a low pass which leads into the basin from the Tanzilla River, a tributary of the Stikine.