Rivers and lakes

About 62% of the territory covered by the branching river network belongs to the Black Sea catchment basin. The longest Croatian rivers, the River Sava (562 km) and River Drava (505 km) also belong to this catchment basin, as does the Danube, into which they both flow. These three rivers to a large extent form natural borders.

The main tributaries of the Sava are the Sutla, Krapina, Kupa (the longest river whose entire course is inside Croatia), Lonja and Una. The main tributaries of the Drava are the Mura, Bednja and Karašica, while the River Vuka flows into the Danube. Most rivers have a high water table in winter and a low one in summer, except the Drava and Mura. The main navigable waterway is the Danube. The Drava is navigable by larger vessels as far as Osijek, and the Sava as far as Sisak.

Hydrographic map
The Danube near Vukovar, one of the main inland waterways of Europe.
Majer's Spring, one of several sources of the River Gacka, an underground river in Lika, famous for its trout farms.
Baćina Lakes, near Ploče in Dalmatia is an area of the National Ecological Network (part of the EU ecological network Natura 2000).

In the Adriatic catchment basin region which covers 38% of the territory, due to the predominant limestone formations, the hydrographic network is less diversified, and rivers spring from copious sources, run more steeply downstream and have shorter courses. The larger among them are the Mirna, Zrmanja, Krka and Cetina, while the largest is the Neretva, although it flows through Croatia for only 20 km, and is navigable at that point. The karst underground streams of the Lika and Gacka also belong to the Adriatic catchment basin.

The mouth of the River Cetina, near Omiš. Several hydroelectric plants have been built on the Cetina, and one of these, Zakučac, not far from Omiš, has the highest production capacity in the country.
Lake Vransko, between Zadar and Šibenik, the lake with the largest surface area in the country; it forms a rich ornithological habitat and is home to fish (eels); since 1999 it has been a nature park.
The River Korana, a tributary of the Kupa, south of Karlovac, one of the rivers belonging to the Black Sea confluence which flow through the karst region of the country.
Zrmanja, carved into the karst plateau in the hinterland behind Zadar.

There are lakes in all parts of the country, but most of them have small surface areas. The largest is Lake Vransko (30.7 km²), a natural lake near Biograd. The world famous, picturesque Plitvice Lakes are in Lika. Artificial lakes built for hydroelectric plants include Lake Dubrava (17.1 km²) and Lake Varaždin (10.1 km²) on the River Drava, and Lake Peruća (13 km²) on the River Cetina.

In terms of the proportion of surface and underground water reserves in the country, Croatia ranks near the top globally, while in terms of the size of its per capita water reserves, it is the third in Europe, behind Iceland and Norway.