The Altmühl is a river in Bavaria, Germany. It is a tributary of the Danube and 230 km in length.

The source of the Altmühl is located close to the city of Ansbach. From here the river runs southeastwards as a narrow brook to enter the Altmühlsee (a lake) north of Gunzenhausen . After leaving Gunzenhausen the river describes a broad curve through the Frankish Alb. It enters the Altmühl Valley Nature Park, which is famous for its natural beauty: The meanders of the Altmühl River have cut deep gorges into the mountains of the Frankish Alb.

The Altmühl passes the cities of Treuchtlingen , Eichstätt and Beilngries . Behind Beilngries the river bed was straightened and integrated into a canal connecting Main and Danube. In spite of protests by conservationists this canal was opened in 1992 and destroyed much of the beauty of the eastern Altmühl Valley.

The Altmühl finally meets the Danube in Kelheim.