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
Euphrates of , the Atatürk Dam reservoir is large enough to hold the entire annual discharge of the Euphrates. Completion of GAP was scheduled for 2010 but has been delayed because the World Bank has withheld funding due to the lack of an official agreement on water sharing between Turkey and the downstream states on the Euphrates and the Tigris. Apart from barrages and dams, Iraq has also created an intricate network of canals connecting the Euphrates with Lake Habbaniyah, Lake Tharthar, and Abu Dibbis reservoir; all of which can be used to store excess floodwater. Via the Shatt al-Hayy, the