Klöntalersee is a natural lake in the canton of Glarus, Switzerland and covers the major part of the Klöntal valley floor.

Since 1908, it has been used as a reservoir for electricity production.

The dam's construction substantially increased the lake's volume.

Klöntalersee is drained by the Löntsch, a left tributary of the Linth.

This article related to a lake in the canton of Glarus is a stub.