The Shellmouth Reservoir (also known as Lake of the Prairies) is a man-made reservoir on the Assiniboine River in Manitoba and Saskatchewan, Canada. The Shellmouth Dam (50°57′49″N 101°25′07″W / 50.96361°N 101.41861°W) is a multi-purpose, embankment dam built by the Prairie Farm Rehabilitation Administration (PFRA). Asessippi Provincial Park is established around the southern arm of the lake.