Lac du Vieux Émosson

Not to be confused with Lac d'Émosson.

Lac du Vieux Émosson is a reservoir in Valais, Switzerland, in the municipality of Finhaut at an elevation of 2205 m. The lake drains into the reservoir Lac d'Émosson, 300 m below.

Lac du Vieux Émoson
Lac du Vieux Émoson Show map of Canton of Valais Lac du Vieux Émoson Show map of Rhône-Alpes Lac du Vieux Émoson Show map of Switzerland Lac du Vieux Émoson Show map of France Lac du Vieux Émoson Show map of Alps
Location	Valais
Coordinates	46°3′45″N 6°53′21″E
Catchment area	4.6 km2 (1.8 sq mi)
Basin countries	Switzerland
Max. length	1.5 km (0.93 mi)
Surface area	0.55 km2 (0.21 sq mi)
Max. depth	42 m (138 ft)
Water volume	13.8 million cubic metres (11,200 acre⋅ft)
Surface elevation	2,205 m (7,234 ft)

In September 2014, an increase of the dam by 21.5 meters was completed. The capacity of the lake was thus doubled to 25 million m³. The larger capacity is used for the Nant de Drance pumped storage plant, for which Lac du Vieux Emosson forms the upper basin and Emosson reservoir the lower basin.^[1] The storage power plant went into operation on 1 July 2022, after 14 years of construction. The construction of the plant cost the equivalent of 2 billion euros. The installed capacity is 900 MW, and 20 GWh can be stored.^[2]

The arch dam Vieux Émosson was completed in 1955. Efforts to raise the dam 20 m (66 ft) began in 2013. The lake forms the upper reservoir for the 900 MW Nant de Drance Hydropower Plant which began operations in 2022.^[3]

See also

• List of lakes of Switzerland
• List of mountain lakes of Switzerland