List of tributaries of the Danube
The Danube is Europe's second-longest river. It starts in the Black Forest in Germany as two smaller rivers—the Brigach and the Breg—which join at Donaueschingen, and it is from here that it is known as the Danube, flowing generally eastwards for a distance of some , passing through several Central and Eastern European capitals, before emptying into the Black Sea via the Danube Delta in Romania.
Topography of Romania
After entering the country in the southwest at Bazias, the Danube travels some 1,000 km through or along Romanian territory, forming the southern frontier with Serbia and Bulgaria. Virtually all of the country's rivers are tributaries of the Danube, either directly or indirectly, and by the time the Danube's course ends in the Black Sea, they account for nearly 40 percent of the total discharge. The most important of these rivers are the Mureş River, the Olt River, the Prut, the Siret River, the Ialomiţa River, the Someş River, and the Argeş River. Romania's rivers primarily flow east, west, and south from the central crown of the Carpathians. They are fed by rainfall and melting snow, which causes considerable fluctuation in discharge and occasionally catastrophic flooding. In the east, river waters are collected by the Siret and the Prut. In the south, the rivers flow directly into the Danube, and in the west, waters are collected by the Tisza on Hungarian territory.