The first hydroelectric dam in the Val de Dix in the Swiss Alps was built from 1929 to 1935 at an elevation of 2,400m above sea level. The complex was enlarged with the Cleuson dam in the Nendaz valley in 1951, which stored water to pump to the Dix. Then from 1951 to 1961 the Grande Dixence Dam was built, which at 700-m long and 285-m high was for half a century the world’s tallest dam. It remains the tallest gravity-type dam in the world. This submerged the earlier dam to create the largest reservoir in Switzerland. Its power stations generate 2,000 GWh a year. The road to the dam is closed in winter due to snow. In summer, visitors can see an exhibition about the construction of the dam and can take special tours in the tunnels through the structure. They can reach the crest of the dam by foot or cable-car. There is a hotel and restaurant. Guided tours are also available at the Arolla and Z'Mutt pumping stations and the Fionnay, Nendaz and Bieudron power plants.