Lika and Gorski Kotar are marked by several significant rivers draining north towards the Pannonian Basin. Those are the Kupa, tracing the northern boundary of the region, Dobra, Mrežnica and the Korana—forming travertine barriers and waterfalls before discharging into Kupa in area of Karlovac, as well as Una, in the eastern part of the region, at the border of Bosnia and Herzegovina. Furthermore, there are losing streams such as Gacka, Krbava and Lika rivers, reflecting a high degree of karstification of the terrain in the region, resulting in increased permeability of soil and rocks. Ingress of water underground resulted in formation of subterranean watercourses and lakes. Probably the finest example of interaction of karst terrain and watercourses in the area are Plitvice Lakes—16 interlinked lakes between Mala Kapela and Plješevica, through which Korana River flows. The area is abundant in travertine barriers, waterfalls and caves of biological origin—created through deposition of calcium carbonate through agency of moss, algae and aquatic bacteria. The Plitvice Lakes are listed as a UNESCO World Heritage Site, and they are a part of one of three Croatia's national parks located in the Mountainous Croatia, along with Risnjak and Sjeverni Velebit.