The Rainy River is a river, approximately 137 miles long, forming part of the Canada–United States border separating Northwestern Ontario and northern Minnesota. The river issues from the west side of Rainy Lake and flows generally west-northwest, between International Falls, Minnesota, and Fort Frances, Ontario, and between Baudette, Minnesota, and R…The Rainy River is a river, approximately 137 miles long, forming part of the Canada–United States border separating Northwestern Ontario and northern Minnesota. The river issues from the west side of Rainy Lake and flows generally west-northwest, between International Falls, Minnesota, and Fort Frances, Ontario, and between Baudette, Minnesota, and Rainy River, Ontario. The Couchiching First Nation is associated with this river, where it had traditional territory.