The Rapid River is a river in Algoma District, Ontario, Canada. The river is about long and begins at Seymour Lake at an elevation of . It travels west and takes in its left tributary the Little Rapid River at an elevation of . The river continues west over a small rapids and a waterfall before emptying into the Mississagi River at an elevation of . A road, which begins at Highway 129 north of the river's mouth, parallels the majority of the river to Seymour Lake. See also List of rivers of Ontario References Rivers of Algoma District