Crna River (Bosnian: Crna rijeka / Црна ријека, "Black River") is the only larger left tributary of Ilomska River. It originating from Duboki jarak ("Deep trench"), altitude of 1380 m, below the hill Blatnica Hill. In upper waterflow it goes to south-east, between Omanjača (right bank, 1355m) and the Ravan (Plain, 1304 m) on Runjavica (1350 m), above the eponymous village (Blatnica). After leaving the ravine, the river flows around Jove masiff turn right to the north to the mouth.
During the Austro-Hungarian rule, along the Crna River (as with Ilomska) built forest narrow-gauge railway to the turntables in 1178 for the exploitation of forest resources, which turnstile at this place as always abounds. Even today there performs intensive felling spruce and fir trees.