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
Karasu (Euphrates) through a rocky gorge. Near the small town of Kemaliye it receives its last tributary, the Çaltısuyu, before turning sharply southeast to flow through a deep canyon into the Keban Dam Lake on the Euphrates. Before construction of the Keban Dam the Karasu joined the Murat River 10 km above the dam site and 13 km above the town of Keban. In 1996, 15 Turkish soldiers were killed when their personnel carrier fell into the river during a routine crossing. When temperatures in Turkey dropped below -25 °C in 2005 the river froze over and was used as a football