During the August 2002 European flood, parts of St. Johann in Tirol were affected by the flood due to high water levels of Kitzbühler Ache and Reither Ache.
Its main tributaries, apart from its headstreams, are the Kitzbühler, Fieberbrunner and Reither Ache, shortly before Kössen the Schwarzlofer from Reit im Winkl, and in Kössen the Kohlenbach and Weißenbach from the lake of Walchsee.
From the waterfall the Rettenbach forms the boundary between the parishes of Going am Wilden Kaiser and St. Johann in Tirol and discharges in Rettenbach into the Reither Ache river.