The Isar is a river in Tyrol (Austria) and Bavaria (Germany) that is not navigable for watercraft larger than rafts. It flows from the right into the Danube south of Deggendorf after a 292 km long course.
It rises in the Alps in the Tyrolean part of the Karwendel in the Hinterautal, and after about 22 km[2] below Scharnitz it crosses the state border into Bavaria, where it flows in the Alps, first through Mittenwald, then through Krün, Wallgau and in the so-called Isarwinkel through Lenggries and Gaißach. It reaches the Alpine foothills at the beginning of the middle course near Bad Tölz, followed by the towns of Geretsried, Wolfratshausen, Munich, Freising and Moosburg. The lower course flows through Landshut, Dingolfing, Landau an der Isar and Plattling.
The Isar flows into the Danube five kilometers south of Deggendorf. Its former form as a typical mountain and pre-Alpine river with a wide, constantly shifting riverbed, extensive gravel banks and branching river arms is only found in certain areas of the upper reaches. After the Danube, the Inn and the Main, the Isar, with its catchment area of 8964.57 km²[2], which lies mostly in Bavaria, is the fourth largest river in this federal state.
The most important tributary is the Amper, which flows into Moosburg, followed by the Loisach, which flows into Wolfratshausen.