Lake Bohinj, the largest natural permanent lake in the Triglav National Park and in Slovenia, is of tectonic origin. The canyon in which it lies was formed by the Bohinj glacier. The main tributary of the lake is the Savica, which collects water in the Triglav Lakes Valley. The lake changes water three times a year. The outlet of the lake is called Jezernica and is one of the shortest rivers in Slovenia. After its confluence with the Mostnica River, it is renamed the Sava Bohinjka.