Tisza, river, eastern Europe, important affluent of the Danube, the chief river of Hungary. It is formed by the confluence of two streams, the Black Tisza and the White Tisza, in the Carpathian Mountains of Ukraine. It winds 970 km (600 mi) northeast, southwest, and finally south, joining the Danube in northern Serbia (part of the republic of Serbia and Montenegro) after running parallel to it for 483 km (300 mi). The river is famous for its fish.