Klöntalersee

Klöntalersee is a natural lake in the Klöntal valley in the canton of Glarus, Switzerland. It was formed by a rockslide and has been used as a reservoir for electricity production since 1908.^[1] Located at an elevation of 848 metres above sea level, the lake covers an area of approximately 3.3 square kilometres.^[1] It is considered the oldest major reservoir in Switzerland and is known for its mirror-like surface that reflects the surrounding mountains.^[1] The primary inflow is the Klön stream, and the outflow is the Löntsch, which flows into the Linth near Netstal.^[1]

Klöntalersee
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Location	Canton of Glarus
Coordinates	47°1′32″N 8°58′50″E
Primary inflows	Chlü
Primary outflows	Löntsch
Basin countries	Switzerland
Surface area	3.3 km2 (1.3 sq mi)
Max. depth	49 m (161 ft)
Surface elevation	848 m (2,782 ft)
Settlements	Seerüti, Vorauen

History

Beginning in 1550, closed seasons for fishing were introduced at Klöntalersee to protect its fish stocks.^[2] During the 18th century, timber from surrounding forests was transported via the lake and floated downstream toward the Walensee.^[2] From 1860 to 1953, ice was harvested from the lake for cooling purposes and distributed to Netstal, Glarus, and other areas.^[2] Between 1905 and 1908, a 21.5-metre-high earth dam was constructed at the eastern end of the lake, significantly increasing its volume and enabling its use as a reservoir for hydroelectric power.^[2][3]

A 2021 study by the Swiss Federal Institute of Aquatic Science and Technology (Eawag), reported by Swissinfo, identified Klöntalersee as one of several mid-altitude Swiss lakes at risk of losing its winter ice cover this century if global temperatures rise by more than 2°C.^[4] Reduced ice cover could lead to changes in lake stratification and water mixing patterns, potentially affecting oxygen distribution and aquatic ecosystems.^[4]

In May 2025, the Glarus Landsgemeinde approved three annual car-free Sundays at Klöntalersee. Starting in 2026, the area will be closed to motor vehicles on the last Sundays of June, July, and August, allowing access only to hikers and cyclists.^[5]

See also

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