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
Kern River of the Central Valley Project, joins the river about west of downtown Bakersfield. The Kern River is one of the very few rivers in the Central Valley which does not contribute water to the Central Valley Project (CVP). However, water from the CVP, mainly the Friant-Kern Canal, will be deposited for water storage in the aquifers. Historically, the river flowed an additional south through a now-dry distributary to Arvin, where it formed the seasonal Kern Lake, which would grow to cover about during wet periods. Water from Kern Lake would then flow west through Buena Vista Slough into Lake Buena