Lake Petnja is artifical lake and is located on the south side of the hill Dilj, about 10 km west of Slavonski Brod and close to place Sibinj. It was created by building of dam in 1968., and it integrated in environment so well it became a part of eco system of Hill Dilj now. Around Lake there is a forest. There are 15 wellsprings which give water to a lake. Because of beautiful blue water color and colorful forests around it, it is called ‘Dilj eye’. Today, Lake is very popular fishing destination (over 8 m depth) and popular resort.
North of this protected site, a source close to the stream Petnja (Vid hill), there are several small caves, among which the most interesting form of erosive canyon Pljuskara seems that, with the cave, and includes three waterfalls on the creek.