Regen (river)

The Regen (German pronunciation: [ˈʁeːɡən]; Czech: Řezná) is a river in Bavaria, Germany, and a left tributary of the Danube, at Regensburg, Germany. The source of its main headstream, the Great Regen (Großer Regen), is in the Bohemian Forest on the territory of the Czech Republic, near Železná Ruda. The river crosses the border after a few kilometres, at Bayerisch Eisenstein. The name in German evolved from the name in Latin, but its meaning is unknown. The Romans called the river variously Regana (feminine gender), Reganus (masculine), and Reganum (neuter).

At Zwiesel, the Great Regen is joined by the Little Regen (Kleiner Regen) to form the Black Regen (Schwarzer Regen). The Black Regen flows through Regen and Viechtach, and is joined by the White Regen (Weißer Regen) in Bad Kötzting. Beyond this confluence, the river is called Regen. The river's total length, including its headstreams, the Great Regen and Black Regen, is 191 kilometres (119 mi). The Little Regen crosses the Frauenau Reservoir.

The Regen Valley forms the main valley crossing the Bavarian Forest; many settlements within the mountains are located along the river. Cities along the Regen river include Cham and Regensburg.