The Varbitsa (Bulgarian: Върбица [vɐrˈbit͡sɐ]) is a 98 km long river in the eastern Rhodope Mountains in southern Bulgaria.

[2][3] The Varbitsa is Bulgaria's most temperamental river, with up to 5,000 times difference in water volume between spring highs and autumn lows, with frequent massive flooding and erosion as a result.

[3] The main stem of the Varbitsa is the river Erma reka, which takes its source in the western Rhodope Mountains at an altitude of 1,284 m on northern foothills of the summit of Margazyan (1,346 m) on the Bulgaria–Greece border, some 2 km southwest of the village of Marzyan.

[3] It initially flows eastwards until the road Madan–Zlatograd, when it turns southeast and runs through a narrow deep valley covered with dense deciduous forests.

There are 15 settlements along its course, 14 villages and one town — Marzyan, Erma Reka and Zlatograd (town) in Smolyan Province, and Preseka, Mogilyane, Benkovski, Erovete, Vurli dol, Barzeya, Krilatitsa, Fotinovo, Stareyshino, Vurben, Ptichar, Sedlari and Gluhar in the municipalities of Kirkovo, Momchilgrad, Dzhebel and Kardzhali Kardzhali Province.