Engstlensee is a natural lake used as a reservoir in the municipality of Innertkirchen , Bernese Oberland, Switzerland . It is located near Joch Pass at an elevation of 1850 m. It can be reached by gondola and by foot from Titlis .

The reservoir has a volume of 10.7 million m³ whereof 2 million m³ are used for electricity production. The lake's surface area is 44 ha (110 acres).

The water of the Engstlensee passes through a tunnel in the neighbouring Gadmental valley before being used in the Fuhren, Hopflauenen and Innertkirchen power stations.