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.

• List of lakes of Switzerland
• List of mountain lakes of Switzerland

• Media related to Klöntalersee at Wikimedia Commons
• Karin Marti-Weissenbach: Klöntal in German, French and Italian in the online Historical Dictionary of Switzerland, 2006-02-28.