The Loisach (German pronunciation: [ˈlɔʏzax] ) is a river that flows through Tyrol, Austria and Bavaria, Germany. The Loisach runs through the great moors Murnauer Moos and Loisach-Kochelsee-Moore

The Loisach is a 113-kilometre-long (70 mi) left tributary to the Isar whose source is near Ehrwald in Austria. It flows past Garmisch-Partenkirchen and into the Kochelsee. At this lake, the water that was diverted from the upper river Isar for the Walchensee Hydroelectric Power Station 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.