| Lake of the Prairies | |
|---|---|
| Shellmouth Dam | |
| Location | Shellmouth-Boulton / Shell River, Manitoba and Cote No. 271, Saskatchewan |
| Lake type | reservoir |
| Primary inflows | Assiniboine River, Shell River (Saskatchewan), Cupar Creek |
| Primary outflows | Assiniboine River |
| Basin countries | Canada |
| Water volume | 480,000,000 m³ |
| Surface elevation | 425 m (1,394 ft) |
The Shellmouth Reservoir is a man-made reservoir on the Assiniboine River in Manitoba and Saskatchewan, Canada.
The Shellmouth Dam an embankment dam was built by the Prairie Farm Rehabilitation Administration (PFRA). Construction started in 1964 and was completed in 1972 costing $10.8 million. The dam is 70 feet (21 m) high and 4,200 feet (1,300 m) long. The reservoir is 35 miles (56 km) in length and stores 390,000 acre foot (480,000,000 m3) at it full supply level of 1,408.5 feet (429.3 m). Outflows are controlled by three gated conduits and a 210-foot (64 m) wide concrete chute spillway.
The dam and reservoir are part of a strategy to reduce the risk of flooding on the Assiniboine River and in Winnipeg. For example, in the 1997 Red River Flood, the inflow to the reservoir peaked at 10,000 cubic feet per second (280 m3/s) while the outflow never exceeded 1,700 cu ft/s (48 m3/s). 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.
The reservoir is also known by the name "Lake of the Prairies". Asessippi Provincial Park is established around the southern arm of the lake.
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.