Slovakia has a dense river network, 96% of which belongs to the Danube catchment area (Black Sea catchment area), and the remaining 4% to the Vistula catchment area (Baltic Sea catchment area).

An excerpt from the article 37 facts about Slovakia

The largest rivers in Slovakia are the Danube, Váh, Hron, Morava, Bodrog, Latorica, and Laborec. The longest river is the Váh - 403 km, and the shortest is Čierna Voda. Most rivers flow in the Slovak mountains. Some flow only through Slovakia, and others form a natural border with neighboring countries (over 620 km), e.g. Dunajec in the north, the Danube in the south, and Morava in the west. The total length of rivers in Slovakia is 49.774 km.