chief river of central Morocco, rising in the Middle (Moyen) Atlas mountains and flowing generally westward for 345 miles (555 km) to the Atlantic Ocean near Azemmour. Although not navigable, it is a perennial, torrential river and a major source of hydroelectric power and irrigation: dams on the river include Afourer, Kasba Zidania, Im Fout, Daourat, Sidi Saïd Maachou, and Bine el-Ouidane (on the El-Abid River). The Tessaout and El-Abid, both of which join the Oum er-Rbia from the south, are the main tributaries. Agricultural products grown in the river's basin include citrus fruits, wheat, grapes, cotton, and flax.