Oum Er-Rbia (Arabic: أم الربيع‎, the mother of spring; original name in Berber is Wansifen, وانسيفن, according to scholars the name was only changed recently, c. 16th or 17th century, and a nearby village called Oum Rabia might have influenced this change) is a river in central Morocco. The river is 555 km long. With an average water debit of 105 m³/s, Oum Er-Rbia is the second-largest river in Morocco after the Sebou River. It originates in the Middle Atlas and passes through the city of Khénifra, arriving at its mouth at the Atlantic Ocean at the port of Azemmour, located on its left bank. Oum Er-Rbia has six dams, the most important of which is Al Massira Dam.