Bohinj or the Bohinj Basin is a 20 km long and 5 km wide basin within the Julian Alps, in the Upper Carniola region of northwestern Slovenia. It is traversed by the Sava Bohinjka river. Its main feature is the periglacial Lake Bohinj. Bohinj is part of the Municipality of Bohinj, the seat of which is Bohinjska Bistrica.
The basin consists of four regions: the Lower Valley Upper Valley Ukanc Basin and Nomenj Basin. It is bounded by the Komarča head wall on one end and Soteska Canyon at the other. The Lower Bohinj Mountain Range represents its southern border. The Sava River has carved a canyon between the Jelovica and Pokljuka plateaus in the east. To the north, Mount Triglav, Slovenia's highest mountain, is also a part of the municipality.
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 Jezrnica 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.