Friedberger Ach
 | |
| The Friedberger Ach about 3.5 km before Thierhaupten | |
| Location | Bavaria,  Germany |
|---|---|
| Reference no. | DE: 1312 |
| Length | 92.48 km |
| Source | near Penzing-Untermühlhausen 48°05′10″N 10°54′19″E / 48.08611°N 10.90528°ECoordinates: 48°05′10″N 10°54′19″E / 48.08611°N 10.90528°E |
| Source height | ca. 600 m |
| Mouth | near Rennertshofen-Stepperg into the Danube 48°44′15″N 11°03′42″E / 48.7375°N 11.061528°E |
| Mouth height | ca. 385 m |
| Descent | ca. 215 m |
| Basin | Danube |
| Progression | Danube → Black Sea |
| Right tributaries | Affinger Bach, Kleine Paar |
The Friedberger Ach is a small river in Bavaria, Germany. It is a right tributary of the Danube. Its source is in the village Untermühlhausen, northeast of Landsberg am Lech. For most of its length it flows parallel to the river Lech at only a few km distance. Towns along the Friedberger Ach include Weil, Prittriching, Mering, Friedberg, Rehling, Thierhaupten and Rain. After Rain, the Friedberger Ach flows east, parallel to the Danube, and joins the Danube near Oberhausen.