Sava

River in the Balkans; length 724 km/450 mi. It rises in the Karawanken Alps and flows southeast across Slovenia and Croatia to join the River Danube, of which it is the chief tributary, at Belgrade in Serbia.

Its principal tributaries, all running south to north, are the Una, Vrbas, Bosna, and Drina. It is navigable for 563 km/350 mi, and was once one of the main trade routes between Western Europe and central Europe and the Black Sea.