Ammersee is a Zungenbecken lake in Upper Bavaria, Germany, southwest of Munich between the towns of Herrsching and Dießen am Ammersee. With a surface area of approximately 47 square kilometres (18 sq mi), it is the sixth largest lake in Germany. The lake is at an elevation of 533 metres (1,749 ft), and has a maximum depth of 81 metres (266 ft). Like other Bavarian lakes, Ammersee developed as a result of the ice age glaciers melting. Ammersee is fed by the River Ammer, which flows as the Amper out of the lake. Like neighbouring Lake Starnberg - deeper, bigger in surface area, similar in shape - it is a popular location for watersports.

Upper Bavaria is one of the seven administrative regions of Bavaria, Germany.