Ukraine has around 23,000 rivers, with most of the rivers draining into the Black Sea and Azov Sea and belonging to the larger Mediterranean basin. Those rivers mostly flow in a southerly direction, except for the Pripyat tributaries in Volhynia and Dniester tributaries in Prykarpattia. A few western Ukraine rivers drain to the north west through Poland to the Baltic Sea, as part of the Western Bug drainage basin. The most notable rivers of Ukraine include the Dnieper, Dniester, Southern Bug, and Siverskyi Donets. The longest river is the Dnieper, the longest tributary is the Dnieper's tributary Desna. Two of the Danube's tributaries in Ukraine, the Prut and the Tysa, are longer than the main river within Ukraine.
In 2013, in accordance with the Water Framework Directive (WFD), the territory of Ukraine has been divided into nine hydrographic zones according to major river basins, including the basins of the Vistula (Western Bug and San), Danube, Dniester, Southern Bug, Dnieper, Don, the rivers of the Black Sea littoral, the Sea of Azov littoral, and separately the rivers of Crimea. The biggest river basin by area is the Dnieper which is subdivided into the Pripyat basin, Desna basin, basin of Middle Dnieper, basin of Lower Dnieper. Beside Dnieper, basin of the Danube zoning is also subdivided into basin of Tysa, basin of Prut and Siret, and basin of the Lower Danube.
