Due to configuration of the terrain, natural lakes are sparse and small; most of them are located in the lowlands of Vojvodina, like the aeolian lake Palić or numerous oxbow lakes along river flows (like Zasavica and Carska Bara). However, there are numerous artificial lakes, mostly due to hydroelectric dams, the biggest being Đerdap (Iron Gates) on the Danube with 163 km2 on the Serbian side (a total area of 253 km2 is shared with Romania); Perućac on the Drina, and Vlasina. The largest waterfall, Jelovarnik, located in Kopaonik, is 71 m high. Abundance of relatively unpolluted surface waters and numerous underground natural and mineral water sources of high water quality presents a chance for export and economy improvement; however, more extensive exploitation and production of bottled water began only recently.