Caumasee, Mountain lake in Flims, Switzerland

Caumasee is a lake in the Flims forest in the canton of Grisons, Switzerland, lying at about 997 metres in a basin of the Flims rockslide. Its opaque turquoise water covers 10.3 hectares and holds a wooded island of roughly 3,000 square metres near its middle. Dense conifers descend to the shoreline, and a small rocky islet with thin stems breaks the surface near the bank.

Caumasee lies in the debris of the Flims Rockslide, the largest prehistoric landslide in the Alps, which left the agriculturally useless terrain to forest. The lake occupies one of several hollows in this hummocky ground, together with Lag Prau Pulté, Lag Prau Tuleritg and Crestasee. In 1835 a bathing hut was built on the north-eastern shore, with a pump feeding three pools and a shared tub; it fell apart within a few years.

The Romansh name Lag la Cauma comes from cauma, meaning a place where cattle rest at midday, from Latin cauma for the heat of the sun. The lake's water was long held to be healing: in the 19th century the sick came to treat eye and skin ailments, gout and unhealed wounds, and in 1835 a bathing hut with a pump fed three pools and a shared tub on the north-eastern shore.

The lake is reached on foot or by bike; the main path from Flims-Waldhaus to the funicular is the only one in the Grosswald where cycling is banned. The Caumasee-Lift, a 125-metre funicular on its 1937 tracks, runs free of charge and since 14 December 2024 also in winter. The walk from the edge of town to the lift takes about ten minutes.

The western bay stays ice-free all winter, even in the longest cold spells, probably because underground water flows into that part of the lake. Dye tests were run in earlier years to trace the water's path, but they failed to establish it.