The Amper, called the Ammer upstream of the Ammersee, through which it runs, is the largest tributary of the Isar in southern Bavaria, Germany.
It flows generally north-eastward, reaching the Isar in Moosburg, about 185 kilometres (115 mi) from its source in the Ammergau Alps, with a flow of 45 m³/s. Including its tributary, Linder, it is 209.5 km (130.2 mi) long.
Major tributaries are the Glonn, which rises near Augsburg; the Würm, which is the outflow of Lake Starnberg; and the Maisach.
