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 politics in the Jordan River basin Water quality is variable in the river basin. The three tributaries of the upper Jordan have a low salinity of about 20 ppm. The salinity of water in Lake Tiberias ranges from 240 ppm in the upper end of the lake (marginal for irrigation water), to 350 ppm (too high for sensitive citrus fruits) where it discharges back into the Jordan River. The salt comes from the saline subterranean springs. These springs pass through the beds of ancient seas and then flow into Lake Tiberias, as well as the groundwater sources that feed into the lower Jordan. Downstream of Tiberias,