Seymour Lake is a lake in the Lake Huron drainage basin in Algoma District, Ontario, Canada. It is about 1.7 kilometres (1.1 mi) long and 0.9 kilometres (0.6 mi) wide, and lies at an elevation of 411 metres (1,348 ft), 60 kilometres (37 mi) northwest of the community of Elliot Lake. The lake is the source of the Rapid River, which flows via the Mississagi River to Lake Huron.