The
Regen (; ) 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).