Lake Sarnen (German: Sarnersee) is a lake in the Swiss canton of Obwalden.

The municipalities of Sarnen and Sachseln are located on the shores of the lake, and the Brünig railway line follows the eastern shore.

[1] The lake's area is about 7.5 km2 (2.9 sq mi) and its maximum depth is 51 m.[1] It is about 5.7 km (3.5 mi) long and, at its widest, 1.6 km (0.99 mi) wide.

[1] The lake is the subject of a watercolour painting by J. M. W. Turner, The Sarner See, Evening, c.

This article related to a lake in Obwalden is a stub.