The entire Slavonia belongs to the Danube basin and the Black Sea catchment area, but it is divided in two sub-basins. One of those drains into the Sava—itself a Danube tributary—and the other into the Drava or directly into the Danube. The drainage divide between the two sub-basins runs along Papuk and Krndija mountains, in effect tracing the southern boundary of the Virovitica-Podravina County and the northern boundary of Požega-Slavonia County, cuts through the Osijek-Podravina County north of Đakovo and finally bisects the Vukovar-Syrmia County running between Vukovar and Vinkovci to reach Fruška Gora southwest of Ilok. The Entire Brod-Posavina County is located in the Sava sub-basin.