It is a river with a more pronounced karst character and typical greenish colour. Its waters are one of the most attractive flyfishing destinations in Europe. The Idrijca enters the Tolmin fishing district in the village of Stopnik. Until it reaches the village of Trebuša, it runs between heavily forested banks, through deep pools, rapids and straits.
At Trebuša, its current slows down and gravel deposits appear. The pools are still long and deep, especially those by the village of Slap ob Idrijci; however, the straits and rapids are slower and gentler. At the village of Bača pri Modreju, it enters the Doblar reservoir and then, at Most na Soči, it flows into the Soča.
The entire length of the river – 16.2 km – is open to fishing. All the species of fish found in the Tolmin fishing district can also be found here: all species of trout, even the large marble trout, grayling, Cottus gobio, Adriatic chub, schools of Italian barbel, Barbus meridionalis caninus, Leuciscus souffia muticellus, common minnow and Austropotamobius torrentium.