The Sava Bohinjka (which merges with the Sava Dolinka into the Sava) begins when two rivers, the Jezernica and the Mostnica, merge. The Mostnica comes from the Voje Valley, whereas the Jezernica is a very short river that flows from Lake Bohinj. Many smaller streams flow into the lake. The largest of them, the Savica, emerges in Komarča as a large waterfall. Savica Falls () gets most of its water from Black Lake (), which is the largest in the Triglav Lakes Valley ().