Lake Bohinj is 4.2 km (2.6 mi) long and 1 km (0.62 mi) at its maximum width. It is a glacial lake dammed by a moraine.
Passenger tourboat on Lake Bohinj
The largest of the streams that flow into the lake, the Savica ('little Sava'), is fed from Črno jezero (Black Lake), the largest lake in the Triglav Lakes Valley. The outflow at the eastern end is the Jezernica creek which merges with the Mostnica to form the Sava Bohinjka, which in turn becomes the larger Sava River at the confluence with the Sava Dolinka. As found out already by Belsazar Hacquet in the 18th century, much more water leaves Lake Bohinj than enters it, which is explained with subterranean sources of water.
^Royal Geographical Society (1856) "Wocheiner-See" A Gazetteer of the World: or, Dictionary of geographical knowledge, compiled from the most recent authorities, and forming a complete body of modern geography -- physical, political, statistical, historical, and ethnographical A. Fullarton, Edinburgh, Scotland, p. 529, OCLC 20348227; note that Lake Bohinj was formerly known in English by its German name Wocheiner See, or sometimes Lake Wochein.
^Baedeker, Karl (1879) "Terglou: The Valley of the Wocheiner Save" The Eastern Alps: Including the Bavarian Highlands, the Tyrol, Salzkammergut, Styria, and Carinthia (4th ed.) Dulau and Co., London, p. 353, OCLC 4018143