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 water into the depression that is now Lake Habbaniyah. Iraq's largest dam on the Euphrates is the Haditha Dam; a earth-fill dam creating Lake Qadisiyah. Syria and Turkey built their first dams in the Euphrates in the 1970s. The Tabqa Dam in Syria was completed in 1973 while Turkey finished the Keban Dam, a prelude to the immense Southeastern Anatolia Project, in 1974. Since then, Syria has built two more dams in the Euphrates, the Baath Dam and the Tishrin Dam, and plans to build a fourth dam – the Halabiye Dam – between Raqqa and Deir ez-Zor. The Tabqa