Klöntalersee, Reservoir in Glarus, Switzerland

Klöntalersee is a reservoir in the Canton of Glarus that stretches over 5 kilometers through the valley and measures nearly 50 meters at its deepest point. The water surface mirrors the surrounding mountain slopes and changes color depending on light and weather.

The lake was formed by a rockslide from the Glärnisch side and a landslide from the Dejenstogg flank. Between 1905 and 1908 a 21.5-metre earthfill dam was built at the eastern end, later raised to 30 metres, making it Switzerland's oldest major reservoir. In 1799 French troops under General Molitor blocked Suvorov's Russians here before withdrawing from Seerüti.

The name of this body of water comes from Klöntal, the valley it fills and whose shape it follows today. The shores draw walkers who stroll along the flat sections or rest at the pebble beaches.

Trains from Zurich to Glarus bring visitors close, from where buses 72 or 504 run several times daily to the valley. The stops lie within walking distance of the shores, and wide paths make access straightforward.

Before ice machines existed, ice was cut commercially from the frozen lake and sold for cooling; the Wädenswil brewery did this for the last time in 1953. The lake also feeds the Löntsch plant near Netstal, where water drops about 365 metres to the turbines through a 4-kilometre pressure tunnel.