The Sava River, a prominent waterway in Central and Southeast Europe, serves as the longest right-bank tributary of the Danube. Its journey traverses Slovenia, Croatia, the border of Bosnia and Herzegovina, and eventually Serbia, culminating in its confluence with the Danube in Belgrade, the Serbian capital. This river delineates the primary northern boundary of the Balkan Peninsula and the southern periphery of the Pannonian Plain. Stretching 990 kilometers (615 miles), the Sava includes the 45-kilometer (28 mi) Sava Dolinka headwater originating in Zelenci, Slovenia. Renowned for its volume of water, it stands as the Danube's largest tributary and ranks second only to the Tisza concerning catchment area (97713km²) and length. Draining a substantial part of the Dinaric Alps, it collects waters from key tributaries like Drina, Bosna, Kupa, Una, Vrbas, Lonja, Kolubara, Bosut, and Krka. This river stands among Europe's longest and most significant tributaries. The population within the Sava River basin is estimated at 8,176,000, shared among three capital cities: Ljubljana, Zagreb, and Belgrade. Approximately two-thirds of the river is navigable for larger vessels, starting from the Kupa confluence in Sisak, a few kilometers below Zagreb.

Sava - Wikipedia