sentences:  Principal among these lakes was Lake Agassiz, a massive lake with a volume rivaling that of all the present Great Lakes combined.Dammed by the northern ice sheet, this lake's immense flow found an outlet in glacial River Warren, which drained south across the Traverse Gap through the valleys now occupied by the Minnesota and Mississippi Rivers.Eventually, the ice sheet melted, and the Red River gave Lake Agassiz a northern outlet toward Hudson Bay.