a river in the Kazakh SSR and Orenburg Oblast of the RSFSR; left tributary of the Ural River. Length, 623 km; basin area, 41,300 sq km. Formed by the confluence of the Karaganda and Zharyk rivers on the western slopes of the Mogodzhars.
The Ilek River valley is characterized by a broad floodplain and many lakes. The flood plain is covered by meadows and, in places, shrub thickets and deciduous forest. The river is fed largely by melted snow. At the village of Chilik, 112 km from the mouth, the average water discharge is 39.8 m3/sec. In the summer the river becomes shallow. The Ilek freezes in the second half of November and thaws toward the end of April. The river’s major tributary is the Khobda (left). The city of Aktiubinsk is located on the Ilek. The river basin contains many phosphorite deposits.