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.
Serbia
Almost all of Serbia's rivers drain to the Black Sea, by way of the Danube river. The Danube, the second largest European river, passes through Serbia with 588 kilometers (21% of its overall length) and represents the largest source of fresh water. It is joined by its biggest tributaries, the Great Morava (longest river entirely in Serbia with 493 km of length), Sava and Tisza rivers. One notable exception is the Pčinja which flows into the Aegean. Drina river forms the natural border between Bosnia and Herzegovina and Serbia, and represents the main kayaking and rafting attraction in both countries.