Karoun River and the tributaries form the largest water basin in Iran covering an area of 60,000 square kilometers.
The 720-km long Karoun arises in Zardkouh in the Zagros Mountains in Chaharmahal-Bakhtiari and enters Khuzestan after flowing through the provinces of Chaharmahal-Bakhtiari and Kohkilouyeh-Bouyerahmad. On its way to the Persian Gulf it flows through the two major cities of Khuzestan, that is, Ahwaz and Khorramshahr, before joining the Arvand-Round waterway, which is also the confluence of the two great Mesopotamian Rivers, the Tigris and the Euphrates.
The Karoun forks into two primary branches on its delta: the Bahmanshir and the Haffar before emptying into the Arvand Roud. The important Island of Abadan is located between these two branches of the Karoun. The port city of Khorramshahr is divided from the Island of Abadan by the Haffar branch.
The northern and eastern parts of the Karoun basin are mountainous, while to its southwest lies the Khuzestan plain.
Fertile lands dotted with small and big lakes are found along the course of this river. These lagoons are the winter habitats of the migratory birds from Siberia. The construction of several dams on the Karoun River and its tributaries has contributed to the building of many hydroelectric projects as development of agricultural lands following the victory of the Islamic Revolution in 1979.
The Karoun is ideal spot for boating and canoeing. The Shalo-Mongasht region is one of the most beautiful areas of Khuzestan province. It covers 13,000 hectares and was declared a protected zone in 1998. The mountain peaks of Khuzestan are snow covered during winter, while the climate on the plain is hot and humid. The vegetation is also varied, and among the important trees is Iranian prized chestnut. In addition, the region abounds with various other trees including almond, wild fig, thyme, and wild celery. Among the animal life of the mountains of Khuzestan mention could be made of the leopard, brown bear, Iranian squirrel, and wolves. Bird life includes partridge, swallow and various types of birds of prey such as falcons and hawks.
It is worth knowing that the Shalo-Mangosht protected zone has three big villages, named Shivand, Posht-e Asiab and Noushivand, through which the Shivand River passes.
The Karoun 3 Dam is located near Shivand village, which is often called a hidden paradise since its natural environment has largely remained untouched. The Shimbar area which covers 54,000 hectares is also another protected area of Khuzestan province. This region enjoys humid and mild weather condition with a height of 540 to 2100 meters above sea level.
Mountainous forests, high peaks, chestnut trees and the vast lake of Sad in the middle of the region is considered as the features of this region. The existence of a beautiful lagoon with a vast space of 19 hectares at the center of the region has cast a special image on the area. It is proper to know that Haft Shahidan region with a space of around 9600 hectares has been registered as a protected area since 2002.