The Gradac (Serbian: Градац, Gradac, pronounced [ɡrǎːdats]) is a river in western Serbia, a tributary of the Kolubara. It cuts a canyon in south-north direction with a length of 22.7 km. Its measured water course has a length of about 28 km and a total drop of 187 m. The source of the river Gradac is situated at the foot of the Povlen mountain.
The Gradac river gorge, with its source tributaries, the special characteristics and the degree of preservation, is one of the less well known natural values of Serbia. However, it is very highly rated among exponents of nature protection. It lies south of Valjevo and influent in the Kolubara directly, on the right side[clarification needed]. The river gorge is the habitat of a number of rare plant and animal species. In the river live brook trout, chub, barbel, and crabs. The biggest attraction of Gradac river are undoubtedly the otters. Along the river lay a number of resorts and beaches including Livadica, Ploce, Kriva Vrbe and Sareno platno. Along the river are several watermills and fish ponds located. The railroad from Belgrade to Bar passes through the Gradac river gorge.
The gorge of the river has more than 70 karst caves. The Degurić cave is, according to the latest research[by whom?], the longest and, with its characteristics, the most beautiful cave in the region of the Valjevo karst. In the caves, traces of palaeolithic, and middle ages ancient times have been discovered.