The Karun rises in the Zard Kuh mountains of the Bakhtiari district in the Zagros Range, receiving many tributaries, such as the Dez and the Kuhrang.

Juris Zarins and other scholars have identified the Karun as one of the four rivers of Eden (Gihon), the others being the Tigris, the Euphrates, and either the Wadi al-Batin or the Karkheh.

The Khersan flows into a reservoir from the southeast passin through it in a narrow canyon, now in a northwest direction, past Izeh, eventually winding into the Sussan Plain.

It then bends southwest, bisecting the city of Ahvaz, and south through farmland to its mouth on the Arvand Roud at Khorramshahr, where its water, together with that of the Tigris and Euphrates, turns sharply southeast to flow to the Persian Gulf.

At several points in history, Mesopotamian civilizations such as Ur and Babylon overthrew the Elamites and gained control of the Karun and its surroundings in modern Khuzestan.

In two of several competing theories about the origins and location of the Garden of Eden, the Karun is presumed to be the Gihon River described in the Biblical book of Genesis.

[10] The strongest of these theories, propounded by archaeologist Juris Zarins, places the Garden of Eden at the northern tip of the Persian Gulf, fed by the four rivers Tigris, the Euphrates, Gihon (Karun) and Pishon (Wadi al-Batin).

In 1888, during a period of increasing British influence in southern Iran, Lynch Brothers opened the first regular steamship service on the river linking Khorramshahr and Ahvaz.

In September 2009, three districts of Basra province in southern Iraq were declared disaster-hit areas as a result of Iran's construction of new dams on the Karun.

[14] The dams on the Karun have had a significant effect on the sediment transport and the ecology of the river, and have required the relocation of thousands of residents.