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 () is a multi-purpose, embankment dam built by the Prairie Farm Rehabilitation Administration (PFRA). The dam and reservoir are part of a strategy to reduce the risk of flood damage for Winnipeg and other communities along the Assiniboine River. For example, in the 1997 Red River flood, the inflow to the reservoir peaked at while the outflow never exceeded . The reservoir is also used to supplement flows on the Assiniboine when conditions are dry, ensuring water supply for Brandon, Portage la Prairie, irrigators, and some industries. For example in early August, 2021 the flow in Brandon was a little over 9 cms while the outflow from Shellmouth was 5.7 cms and inflow was less than 0.5 cms. Therefore without the dam the flow in the Assiniboine at Brandon would be a bit under 4 cms. Asessippi Provincial Park is established around the southern arm of the lake. Specifications The dam is high and long. The reservoir is in length and stores 390,000 acre feet (480 million cubic metres) at the spillway crest level of . Outflows are controlled by a gated conduit and a wide concrete chute spillway. The normal summer level target is between and . Fish species Fish species include walleye, yellow perch, northern pike, mooneye, burbot, rock bass, brown bullhead, white sucker, shorthead redhorse and common carp. Rock bass are Saskatchewan's only native bass. Gallery See also List of lakes of Saskatchewan Portage Diversion (Assiniboine River Floodway) Red River Floodway References External links Lake of the Prairies Conservation District Fish Species of Saskatchewan Lake Levels Assiniboine River Cote No. 271, Saskatchewan Lakes of Manitoba Flood control projects Bodies of water of Parkland Region, Manitoba