The Ziller is a right tributary to the Inn, in the Zillertal in Tyrol, Austria. It is 55.7 km long, and its basin area is 1135 km2. It springs from the ridge of the Zillertal Alps, and feeds the Zillergründl Dam. In Mayrhofen it receives the Zemmbach (that in turn receives the Tuxbach). By Zell am Ziller, it receives the Gerlosbach, before flowing into the Inn by Strass im Zillertal. For historical reasons, the Ziller—first mentioned in 927 as Zilare —for most of its course makes up the border between the Diocese of Innsbruck on the west and the Archdiocese of Salzburg on the east. The Ziller today shows a good presence of brown trout and rainbow trout, as well as grayling. It is up to 20 m wide and 2 m deep, and it has an average discharge of 43.1 m3/s.