Regen river

Regen
The Regen near Lappersdorf.
Country	Germany, Czech Republic
Basin features
Main source	Bohemian Forest
River mouth	Danube 49°1′35″N 12°6′13″E / 49.02639°N 12.10361°E / 49.02639; 12.10361Coordinates: 49°1′35″N 12°6′13″E / 49.02639°N 12.10361°E / 49.02639; 12.10361
Basin size	2,953 km2 (1,140 sq mi)
Physical characteristics
Length	169 km (105 mi)
Discharge	Average rate: 40 m3/s (1,400 cu ft/s)

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 Großer Regen ("Big 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 Großer Regen is joined by the Kleiner Regen ("Little Regen") to form the Schwarzer Regen ("Black Regen"). The Schwarzer Regen flows through Regen and Viechtach, and is joined by the Weißer Regen ("White Regen") in Bad Kötzting. Beyond this confluence, the river is called Regen. The river's total length, including its headstreams Großer Regen and Schwarzer Regen, is 169 kilometres (105 mi).

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.