Danube
Classified as an international waterway, it originates in the town of Donaueschingen, in the Black Forest of Germany, at the confluence of the rivers Brigach and Breg. The Danube then flows southeast for about , passing through four capital cities (Vienna, Bratislava, Budapest and Belgrade) before emptying into the Black Sea via the Danube Delta in Romania and Ukraine.
Sava
The Sava (; , , ) is a river in Central and Southeastern Europe, a right tributary of the Danube. It flows through Slovenia, Croatia, along the northern border of Bosnia and Herzegovina, and through Serbia, discharging into the Danube in Belgrade. Its central part is a natural border of Bosnia-Herzegovina and Croatia. The Sava forms the northern border of the Balkan Peninsula, and the southern edge of the Pannonian Plain.