Walchensee, Alpine lake in Kochel am See, Germany

Walchensee stretches across 16.4 square kilometers in the Bavarian Alps and sits in a tectonic valley. Its maximum depth reaches 192.3 meters, making it one of the deepest Alpine lakes in Germany.

Walchensee fills a tectonic depression of the Bavarian Syncline, which makes it one of Germany's oldest lakes; the Isar-Loisach glacier reshaped it during the ice ages. The monasteries of Benediktbeuern and Schlehdorf held the lake by 740, keeping it until secularisation in 1803. The first written record as Walhense dates from the 11th century.

The name comes from Middle High German and referred to romanized inhabitants of the Alpine region. Fishing rights belonged to Benediktbeuern Abbey from 740 until secularization in 1803, when church property passed to the Bavarian state.

The shore offers windsurfing, sailing, scuba diving, and hiking, with 2.5 kilometers (1.5 miles) of beach open to visitors. The water stays cool even in summer, so proper clothing is advisable when swimming.

Sassau Island within the lake serves as a nature reserve and hosts breeding grounds for numerous bird species. Visitors cannot land on the island, but waterfowl and raptors can be observed from the shore.