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
Whiteadder Water and Berwickshire, with water. From there, crossing into Berwickshire it runs alongside the B6355 road to Ellemford where it joins the Dye Water and further on at Abbey St. Bathans, the Monynut Water. By this point having become a much larger body of flow, the Whiteadder meanders across Eastern parts of the Merse passing the communities of Preston, Chirnside, Allanton. Here at Allanton the Whiteadder joins with its antonymic counterpart the Blackadder Water. The river proceeds by Foulden, Edrington, and Paxton, it crosses into England, before joining the River Tweed, just north of East Ord, a suburb of Berwick-upon-Tweed. The