The Altmühl (German pronunciation: [ˈaltˌmyːl] ⓘ, Latin: Alchmona, Alcmana, Almonus)[2] is a river in Bavaria, Germany.

From here the river runs southeastwards as a narrow brook to enter the Altmühlsee [de] (a lake) north of Gunzenhausen.

The Altmühl rises on the southern slope of the Franconian Ridge northeast of Rothenburg ob der Tauber, near the Hohe Leite and about 500m southeast of the Burgbernheim wilderness Wildbad.

As its source, the Royal Bavarian Hydrotechnical Bureau at Munich in 1904 fixed the drainage ditch of Hornauer Weiher.

The water of the Regnitz flows finally over the Main into the Rhine, so that with the transfer an artificial river bifurcation was created.

From Treuchtlingen the Altmühl flows in its lower course through the Franconian Jura plateau, in whose karst limestone it has dug a narrow valley.

On the steep valley slopes here sometimes bizarre rock formations, for instance the cauldron shaped washouts near the village Eßlingen, about 20m above the river level.

From the year 1910 the course of the river downstream from Unterwurmbach was straightened and regulated with numerous weirs, hence many oxbow lakes were cut off.