river in Bulgaria, rising in the central Rhodope Mountains near the town of Smolyan and following a 180-mile (290-kilometre) course eastward past Kŭrdzhali and Ivaylovgrad to enter the Maritsa just west of Edirne, Tur., after a 23-mile (37-kilometre) course in Greece. The Bulgarian section has three hydroelectric and irrigation dams, among the largest in Bulgaria. In the upper valley are the mining towns of Rudozem, Madan, and Smolyan on the tributary Cherna River. The Arda River valley is known for its tobacco growing.