Caumasee (Romansh: Lag la Cauma or Lai da Cauma) is a lake near Flims, in the Grisons, Switzerland. It is one of the lakes on the Flims Rockslide deposits. The lake is fed from underground sources. Its surface area is 10.3194 ha. When the lake is at a low level, with a small volume of water, it warms up sooner than most lakes in the region, so people can be seen starting to swim the lake in April while bigger lakes even in lower areas of Switzerland remain rather cool. Water temperature in summer is at an average 21 Celsius, with a maximum around 24 Celsius.