Lake Sarnen

Lake Sarnen lies on the Obwalden valley floor. Its catchment extends towards Lungern and the Melch valleys, while settlements and transport routes sit close to shore. Rapid inflows and a naturally constrained outlet explain its central role in regional flood protection.

The Dreiwässer Canal, Grosse Melchaa and Kleine Melchaa are major inflows; since 2015 the Kleine Melchaa has entered the lake directly through a new channel. The Sarneraa is the outlet to the Alpnachersee. Steep tributaries can deliver water and debris quickly, while outlet capacity limits how fast the level falls.

Winter snow storage, spring melt and intense summer rain shape the curve. Following past floods, weirs and a relief tunnel are changing the system. Operating rules also consider downstream flood protection towards Lake Lucerne, so interpretation must distinguish natural inflow from the current operating and construction state.

During a rapid rise, direction and speed matter more than the last decimal. Level describes the lake surface while Sarneraa discharge describes water leaving; both may rise at once. Official warnings and local instructions take priority during floods, with Seepegel providing an overview and source links.

Smaller and shallower than the largest Alpine lakes, it responds directly to weather at the surface. Inflows may bring locally cooler, turbid water after rain. A warm reading says nothing about clarity or microbiological bathing quality; relevant cantonal information remains authoritative.