The Osum is a river in southern Albania, one of the source rivers of the Seman. It is long and its drainage basin is . Its average discharge is . Its source is in the southwestern part of the Korçë County, near the village Vithkuq at an altitude of . It flows initially south to the Kolonjë municipality, then west to Çepan, and northwest through Çorovodë where it flows through the famous Osum Canyon, Poliçan, Berat and Urë Vajgurore. It joins the Devoll near Kuçovë, to form the Seman. The discharge of the river is reported to vary between /s and /s.
Name
In classical antiquity, the Osum river was known as the Apsus, which is a derivative of the Indo-European root *ăp- "water, river". The contemporary Albanian name Osum (definite form: Osumi), which is used to indicate the upper course of the river, evolved from *Apsōn(em) through Bulgarian phonetic changes. In Bulgaria there is a river with the same name origin - Osam. Also the contemporary Albanian name Seman/Semen (definite form: Semani/Semeni), which is used to indicate the lower course of the river, evolved from *Apson-, but through Albanian phonetic changes.