The source of the Natisone (Nadiža) is in Italy. The river makes an almost 12-km loop through Slovenia before returning there. Until it reaches the village of Sedlo, it is hidden in a narrow valley full of rapids and deep pools. From that point onwards, however, it enters a widening gravelly valley and almost disappears in its own deep gravel deposits below the village of Robič.
Its waters are inhabited by all species of trout, grayling, Cottus gobio, as well as large numbers of bleak, Adriatic chub, italian barbel, Leuciscus souffia muticellus, Barbus caninus, common minnow as well as Austropotamobius italicus.
