The lake, which is tectonic in nature, was formed when the Bohinj glacier receded. It is 2,120 m long, 1,380 m wide and up to 30.6 m deep.

The lake has no larger natural inflows other than a few small springs. The thermal springs in the north-eastern part of the lake supply water to the swimming pools of the Grand Hotel Toplice, the Park Hotel and the Golf Hotel.