Pivka (river)

The Pivka is a karst lost river in Slovenia. The river is 27 kilometres (17 mi) in length. The Pivka ends in Planina Cave, where it merges with the Rak River and then the Unica River. The confluence of the Pivka and the Rak is one of the largest subterranean confluences in Europe. Rising in limestone country south of Prestranek, it forms part of the classic Dinaric karst system and ultimately feeds the Ljubljanica—and thus the Black Sea basin—after disappearing underground in Postojnska jama. The Pivka created Postojna Cave, the longest cave system in Slovenia as well as one of its top tourism sites.