The Loisach is a 114 km long left tributary to the Isar. The source of the Loisach is near Ehrwald in Austria. The Loisach flows past Garmisch-Partenkirchen and into the Kochelsee. At the Kochelsee the water that was diverted from the upper river Isar for power generation at the Walcheseekraftwerk joins the Loisach. The Loisach then flows out of Kochelsee and joins the Isar at Wolfratshausen. A canal joins the Isar and the Loisach returning the water diverted for power generation to the Isar before Wolfratshausen to reduce the risk of flooding in the town.