Crestasee (Romansh: Lag la Cresta) is a small lake shared by the municipalities of Flims and Trin in the Grisons , Switzerland . From 1892 a guest house on its northern end served as pension and still is a restaurant today in its original state.

There is no tributary to the lake. The rough character of the whole area derives from being a debris area of the gigantic Flims Rockslide, where waters flow underground until feeding lakes at certain spots such as Crestasee, Caumasee or Lag Prau Pulté .

Less than 100 yards (91 m) from its northern end a gorge called "Felsbachschlucht" is formed by river Flem, coming from Flims, whose Romansh name is also Flem. The waters from the lake and river are independent, and of course the river had only some 10 000 years to create the gorge as this is the age of the rockslide.