Idrijca springs under the village Vojsko in the hills above Idrija and is our second largest river. It first flows toward South East to Idrijska bela, making a turn towards Idrija (NE), than slowly turning again towards the Soča valley (NW). Because it springs in the forested hills it has a character of a Karst river with typical green color. Its banks are overgrown with trees to the shore and it has very deep pools with rapids and shallow runs between them. It flows into the HPP reservoir at Bača pri Modreju, joining Soča under Most na Soči. All the native species of fish and rainbow trout are present in this river.

The upper part of Idrijca is managed by the Angling club of Idrija. From the bridge in Stopnik to the confluence with Soča it's managed by the Angling club of Tolmin.