Walchensee or Lake Walchen is one of the deepest and largest alpine lakes in Germany, with a maximum depth of 192.3 metres (631 ft) and an area of 16.4 square kilometres (6.3 sq mi). The lake is 75 kilometres (47 mi) south of Munich in the middle of the Bavarian Alps . The entire lake, including the island of Sassau, is within the municipality of Kochel . The lake and island are owned by the Bavarian State. To the east and the south, the lake borders the municipality of Jachenau .

The name Walchen comes from Middle High German and means "strangers".