The Schmutter is a 96-kilometer-long river in the Bavarian administrative district of Swabia. It rises in the Stauden, about three kilometers west of Siebnach, and flows north through the tertiary hills and the Western Forests Nature Park to the Danube. The mouth of the Schmutter into the Danube near Donauwörth forms the historical end point of the Via Claudia Augusta, the oldest Roman road in the Bavarian Alpine foothills.
Flooding events must be expected on the Schmutter in winter and summer. South of the A8, including in the Schmutter valley near Diedorf, the Schmutter floodplain is flooded several times a year. These conditions place high demands on flora and fauna.
The Schmutter drains parts of the Iller-Lech gravel plates within a strip approximately 68 km long and up to 13 km wide, oriented south-north. In the west, the 507 km² catchment area of the Schmutter borders on that of the Zusam and in the east on that of the Lech.
The Schmutter is an important tributary of the Danube and shapes the landscape of the Bavarian administrative district of Swabia. Its regular floods shape the floodplain landscape and place high demands on flora and fauna. The mouth of the Schmutter into the Danube near Donauwörth forms the historical end point of the Via Claudia Augusta, the oldest Roman road in the Bavarian Alpine foothills.