Veliki Buk, Natural monument and waterfall in Opština Despotovac, Serbia.

Veliki Buk is a waterfall on the Vrelo stream, a right tributary of the Resava, on the limestone slopes of Mount Beljanica in eastern Serbia at about 380 m above sea level. It is an accumulative waterfall formed by the buildup of travertine (bigar): a tall column drops from a rocky ledge and fans out over moss-covered rock into a shallow turquoise pool ringed by travertine blocks, with brown water flowing on over reddish rocks.

The waterfall and the Vrelo spring were protected by a Serbian government decree in 1995 as the natural monument "Lisine", a first-category natural asset and a site of Serbia's geoheritage. Lisine was long considered the country's highest waterfall at 25 metres, until waterfalls on Stara Planina were discovered during the 1990s.

The falls are fed by the Vrelo, whose water comes from the karst plateaus of Beljanica; a direct underground link was established with the sinking rivers of the Rečke and Busovate hollows. The site lies beside Resavska Cave and is protected as the Lisine nature monument, a geo-heritage object of Serbia.

The falls lie at about 380 m above sea level on the Vrelo, a right tributary of the Resava, close to Resavska Cave in Despotovac Municipality. The stream gathers water from the karst plateaus of Beljanica, so flow varies with the season. Approach from the Resava side and combine the visit with the cave.

The waterfall is an accumulation form built by travertine (bigar) deposition, not by erosion. Its 25-metre drop made Lisine the highest waterfall in Serbia until the 1990s, when taller falls were found on Stara Planina. The Vrelo's water comes from the karst of Beljanica, with a direct link to sinking rivers from the Rečke and Busovate hollows.