[1] It rises near Vojsko, flows towards northeast and after passing through Idrija turns to the northwest.

After passing through Spodnja Idrija and Cerkno it joins the Soča in Most na Soči.

[1] The major tributaries are the Belca, Zala, Cerknica, and Bača from the right and the Nikomlja, Kanošica, and Trebušica from the left.

One of the right tributaries is also the Jezernica River, which originates from the Wild Lake (Slovene: Divje jezero).

The river has many fish, among which the Salmo marmoratus, the rainbow trout, and the Grayling are noteworthy.