The Karūn (also spelled as Karoun) is Iran's most effluent, and the only navigable, river. It is 450 miles (720 km) long. It rises in the Zard Kuh mountains of the Bakhtiari district in the Zagros range, receiving many tributaries, such as the Dez and the Kuhrang, before passing through the capital of the Khuzestan province of Iran, the city of Ahvaz.
The Karun continues toward the Persian Gulf, forking into two primary branches on its delta: the Bahmanshir and the Haffar that joins the Shatt al-Arab (Arvand Rud in Persian), emptying into the Persian Gulf. The important Island of Abadan is located between these two branches of the Karun. The port city of Khorramshahr is divided from the Island of Abadan by the Haffar branch.
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 that is described in the Biblical book of Genesis. The strongest of these theories propounded by archeologist Juris Zarins places the Garden of Eden at the northern tip of the Persian Gulf, fed by the four rivers Tigris, Euphrates, Gihon Karun and Pishon (Wadi Al-Batin).
The name of the river is derived from the mountain peak--Kuhrang, that serves as its source.
Famous silent film documentary Grass: A Nation's Battle for Life (1925) tells the story of Bakhtiari tribe crossing this river with 50,000 people and 500,000 animals.
It was here during the Iran–Iraq War that the Iranians stopped the early Iraqi advance. With its limited military stocks, Iran unveiled its "human wave" assaults which used thousands of Basij (Popular Mobilization Army or People's Army) volunteers.