The Isar is a river in Tyrol, Austria and Bavaria, Germany. Its source is in the Karwendel range of the Alps in Tyrol; it enters Germany near Mittenwald, and flows through Bad Tolz, Munich, and Landshut before reaching the Danube near Deggendorf. At 295 km (183 mi) in length, it is the fourth largest river in Bavaria, after the Danube, Inn, and Main. It is Germany's second most important tributary of the Danube after the Inn.
Since the 1920s the water of the Isar has been used for the generation of electricity.