The Alfbach is a 22.3-kilometre-long (13.9 mi), orographically right-bank tributary of the Prüm in the district of Bitburg-Prüm in the German state of Rhineland-Palatinate.

Its source lies on the northern slopes of the Schwarzer Mann (697.8 m above NHN[2]) about three kilometres northeast of Halenfeld in the municipality of Buchet.

The stream flows initially in a southwesterly direction to Halenfeld, where it collects its main tributary, the Donsbach, then turns south as far as Buchet, before changing direction to the southwest to continue through Bleialf.

Continuing mainly in a southeasterly direction the Alfbach empties into the Prüm west of Pronsfeld at a height of 365 m above NHN.

The Alfbach drains a catchment area of 55.693 km2 (21.503 sq mi) ; its waters flowing via the Prüm, Sauer, Moselle and Rhine to the North Sea.