Kučaj (, ) is a mountain range in eastern Serbia. Its highest peak, Velika Tresta has an elevation of 1,284 meters above sea level. They belong to the Serbian extension of Carpathians, which separate the valleys of Great Morava and Timok. Geography The area is a plateau in form, of complex tectonic and morphological structure, subdivided by the river valleys. One of the main features is the Resava Cave. North of Resava Cave is the natural monument Lisine, which comprises two waterfalls, Veliko Vrelo and Veliki Buk. The Lisine hydro-complex and Resava Cave are under one administration. In 2017 the Government of Serbia and Institute for Nature Protection began preliminary actions into creating a new national park, which would cover the mountainous Kučaj-Beljanica region. It is supposed to be the sixth and the largest national park in Serbia encompassing the Resava Cave, Lisine complex and some of the oldest, intact forest in the country, like the Vinatovača rainforest, which remained intact since the mid 17th century. The study on protection was finished in 2020. It concluded that the area is the most forested one in Serbia, and described it as the proper wilderness. Features Sinking rivers The karst region is location of numerous sinking rivers: Kločanica; with the length of , it is the longest sinking river in eastern Serbia. It sinks into the abyss at an elevation of , flows underground for and resurfaces in the Resava valley, at an elevation of . Klencuš; long, it sinks into the chasm at an elevation of and reappears after an underground flow of at an elevation of as the Zlot springs which form the river of Zlotska. Velika Tisnica; it springs at the Beljanica mountain and is long. It disappears at , flows below the ground and springs out again at as Žagubica Spring. From there, it flows as the long Mlava river. Nekudovo; long, sinks at and after springs out at as the source of the Crnica river. Demizlok; it is long and goes underground at in the sinking cave. It resurfaces after at in another cave, Lazareva Pećina, which is the longest explored cave in Serbia. Mikulj; long stream sinks at and after springs out at the Zlot springs. Veliki Buk Watefall Veliki Buk (or Lisine) waterfall is located in the watershed of the Resava River in east Serbia. It is carved in the karst area, where the sinking