Seymour Lake is a lake in the Lake Huron drainage basin in Algoma District, Ontario, Canada. It is about long and wide, and lies at an elevation of , 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. A road, which begins at Highway 129 north of the mouth of the Rapid River, parallels the majority of the river to Seymour Lake