 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.