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, it is the sixth largest lake in Germany. The lake is at an elevation of 533 metres, and has a maximum depth of 81 metres. 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.
Ammersee and the Amper are part of the ancient Celtic amber trading route leading to the Brenner Pass. The word Ammer is a 13th-century form of Amper, the Celtic *ambra, deriving from the Indo-European *ombh-, *mbh- "wet, Water".
Passenger services have operated on the lake since 1879. Today they are operated by the Bayerische Seenschifffahrt company, using a mixture of historic paddle steamers and motor ships.