The lake system is comprised of 16 named and several smaller unnamed lakes, cascading one into the next. Due to the geological substrate and characteristic hydrogeological conditions, the lake system has been divided into the Upper and Lower lakes. The twelve lakes forming the Upper Lakes are: Prošćansko jezero, Ciginovac, Okrugljak, Batinovac, Veliko jezero, Malo jezero, Vir, Galovac, Milino jezero, Gradinsko jezero, Burgeti and Kozjak. These lakes were formed on impermeable dolomite rock, and are larger, with more indented and gentler shores than the Lower Lakes. The Lower Lakes, consisting of the lakes Milanovac, Gavanovac, Kaluđerovac and Novakovića Brod, were formed in permeable limestone substrate, cut into a deep canyon with steep cliffs. The lakes end in the impressive waterfalls Sastavci, with the Korana River springing under the base of the falls.