Tigris–Euphrates river system through the central plain and combine at Al-Qurnah to form the Shatt al-Arab and discharge into the Persian Gulf. The region has historical importance as part of the Fertile Crescent region, in which civilization is believed to have first emerged. The ecoregion is characterized by two large rivers, the Tigris and Euphrates. The rivers have several small tributaries which feed into the system from shallow freshwater lakes, swamps, and marshes, all surrounded by desert. The hydrology of these vast marshes is extremely important to the ecology of the entire upper Persian Gulf. Historically, the area is known as Mesopotamia. As
Water supply and sanitation in Iraq of Iraq. These two rivers account for 98% of Iraq`s surface water supply. Their flow is therefore very vulnerable to dams and water diversions in Turkey, Syria and Iran. The Euphrates does not receive water from permanent tributaries within Iraq territory and is fed only by seasonal runoff from wadis. The average annual flow of the Euphrates at the border to Turkey is estimated at 30 km³, with a fluctual annual value ranging from 10 to 40 km³. The Tigris has an average annual runoff of 21.2 km³. Within Iraq, the Tigris River receives water from five main tributaries, namely