Dams and their associated structures are used to form reservoirs to hold back or store water or mud, and to hold back sediment, ice or snow. The water stored in reservoirs is mainly used for energy production, water supply, irrigation, production of artificial snow, fish farms, reserves for fire-fighting operations and the regulation of water levels in lakes. About 90% of all dams are built to generate hydro-electricity. Because they retain the water when plentiful, they also play an increasingly important role during floods, since they limit the volume of water downstream and thus help reduce damage.
There are 200 major dams under the supervision of the SFOE making an overall total of 222 dams and associated structures. 124 of these dams are in the form of concrete walls (69 gravity dams, 51 curved dams, 2 multiple-curve dams and 2 pierhead dams), while 70 are soil and stonefill constructions, and 28 are river weirs. 25 are over 100 metres in height, and 4 are over 200 metres high, namely the Grande Dixence gravity dam in Val d'Hérémence / VS (285 metres), and the Mauvoisin (Val de Bagnes / VS, 250 metres), Luzzone (Valle di Blenio / TI, 225 metres) and Contra (Valle Verzasca / TI, 220 metres) curved dams. Most of the major dams are located in the Alps.