Mauvoisin Dam is a concrete variable radius arch dam across the Val de Bagnes on the Dranse de Bagnes stream, in the canton of Valais, Switzerland. Initial construction on the dam commenced in 1951 and was completed in 1957, with the reservoir filling by 1958. In 1991, the dam was raised to increase the capacity of the reservoir for winter storage. The dam’s primary purpose is hydroelectric power generation.
The eighth highest dam in the world, Mauvoisin stands 250 metres (820 ft) high and 520 metres (1,710 ft) long, with a structural volume of 2,030,000 cubic metres (2,660,000 cu yd). The impounded water behind the dam forms the 4.9-kilometre (3.0 mi) Lac de Mauvoisin, which has a capacity of 211.5 million m3 (171,500 acre feet) and a full surface area of 208 hectares (510 acres).The dam and reservoir control runoff from a catchment of 167 square kilometres (64 sq mi). Flood waters are released by a gated spillway with a capacity of 107 m3/s (3,800 cu ft/s).