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 Iraq, there are no more natural tributaries to the Euphrates, although canals connecting the Euphrates basin with the Tigris basin exist. The drainage basins of the Kara Su and the Murat River cover an area of and , respectively. Estimates of the area of the Euphrates drainage basin vary widely; from a low to a high . Recent estimates put the basin area at , and . The greater part of the Euphrates basin is located in Turkey, Syria, and Iraq. According to both Daoudy and Frenken, Turkey's share is 28 percent, Syria's is 17 percent and that of Iraq