Cleuson Lake, Reservoir in Nendaz, Valais, Switzerland

Cleuson Lake is an artificial reservoir located above 2,000 meters (6,500 feet) in the Valais region of Switzerland. The dam stretches over 400 meters (1,300 feet) and rises nearly 90 meters (300 feet) high, holding water from the surrounding valley in a distinctive turquoise blue.

The reservoir, originally called Lac de Saint-Barthélemy, was built as part of the Grande Dixence scheme after the Printze was tapped in 1945. Its hollow gravity dam was erected between 1947 and 1949: 87 m high, 420 m along the crest, 84 m wide at the base, using about 300,000 m³ of concrete. Cement arrived by an 11.5 km cableway from Ardon station, and gravel came from the Grand-Désert moraine. No one had to be resettled.

The site is accessible via mountain roads and hiking trails, and visitors should bring water, snacks, and sturdy shoes for the terrain. The area remains cool even in summer, so dress accordingly, and since there are no facilities directly at the lake, plan ahead for your visit.

The dam is hollow: its interior at 2,110 m houses four pumps of 1,400 hp each, moving up to 2.2 m³ per second from the lake up to Lac des Dix. Cement for the 1947–1949 wall arrived by an 11.5 km cableway from Ardon station, in 400 kg cylindrical buckets.