It originates in the Zagros Mountains of western Iran, on the slopes of Zard-Kuh. The river flows south and west through several prominent mountain ridges, and receives additional water from the Vanak on the south bank and the Bazoft on the north. These tributaries add to the catchment of the river above the Karun-4 Dam. downstream, the Karun widens into the reservoir formed by the Karun-3 Dam.