Lac des Toules, reservoir in Valais, Switzerland

Lac des Toules is a reservoir in the Wallis municipality of Bourg-St-Pierre, formed mainly by the Dranse d'Entremont and held back by the Les Toules dam, completed in 1963. Its water level averages 1,810 m above sea level, and the lake runs north-south toward the dam. Because the slopes are steep, the water surface has no arms reaching into the side valleys.

The Les Toules dam was completed in 1963, creating the reservoir that reaches an average level of 1,810 m above sea level. The lake is fed mainly by the Dranse d'Entremont, with the Torrent des Erbets entering from the west and the Torrent de Pieudet from the Mont Vélan massif to the east. In 2021 the reservoir received Switzerland's first floating solar plant on a reservoir, built for 2.35 million francs.

The reservoir lies in the commune of Bourg-Saint-Pierre on the Dranse d'Entremont, and the dam that holds it is called Les Toules. The floating solar plant, in service since 2021, has become the feature people come to see: 1,400 panels on 35 polyethylene platforms, assembled nearby and lifted onto the water by helicopter.

The reservoir lies on Nationalstrasse 21 in the Val d'Entremont, reached from Martigny via Bourg-St-Pierre; the road runs above the eastern shore behind a gallery, while an unpaved path follows the western side. At high water the lake reaches close to the approach lanes of the Grosser Sankt Bernhard tunnel.

The floating solar plant went into operation in 2021, not 2019, and cost 2.35 million Swiss francs. Its 1,400 panels on 35 platforms cover 2% of the lake surface, an area of 2,240 m², with floats of polyethylene and a frame of aluminium. Assembled nearby, the panels were flown onto the platforms by helicopter; the plant supplies about 220 households and is to be enlarged to serve 6,100.