Lake Lungern
Lake Lungern is a natural lake in Obwalden, Switzerland which is named after the town Lungern on its shore. The lake is drained by the Sarner [Aa river], which flows through the Sarnersee and into Lake Lucerne.
The lake was originally much larger, and covered a large part of the valley it is situated in. Starting in 1836, its level was lowered by through an artificial drainage tunnel with a length of. It is used as a reservoir.