Lake Sarnen, Lake in the canton of Obwalden, Switzerland

Lake Sarnen is a natural lake in the canton of Obwalden, in central Switzerland, sitting at around 1,540 feet (470 meters) above sea level. It stretches about 4 miles (6 kilometers) in length and reaches a depth of around 167 feet (51 meters), with forested hills rising on both sides.

At the end of the last Ice Age, Lake Sarnen was still connected to Lake Lucerne. Over time, sediment carried by melting glaciers filled the gap between them, eventually forming two separate lakes.

The lake is shared by the municipalities of Sarnen, Sachseln and Giswil; only a small strip west of the Dreiwässerkanal mouth belongs to Giswil. The Dreiwässerkanal, built in Giswil in 1875, carries water from the Lauibach and the Aa out of Lake Lungern into the lake's southern end. The Brünig railway line runs along the eastern shore.

The eastern shore is easy to reach by train or road, while the northwestern side is only accessible via a narrow track. Visitors who want to walk around the lake can combine hiking on one side with the boat or train on the other to save time.

The lake appears in a watercolour by J. M. W. Turner, "The Sarner See, Evening", painted around 1842. The English painter made it during one of his journeys through central Switzerland, and the view shows the water at dusk.