The Atrek (also Atrak and Etrek) (Persian: اترک, Turkmen: Etrek derýasy) is a fast-moving river which begins from Quchan in the Hezar Masjed mountains of Northeastern Iran (37°10′N 59°00′E), and flows 563 km (350 mi) westward draining into the southeastern corner of the Caspian Sea in Turkmenistan. Because of the high use of its waters for irrigation, it only flows into the Geography
The Atrek is 669 km long and drains a basin of 27 300 km².
Beginning at 37°59′28″N 55°16′29″E, where its tributary the Sumbar join it, the river forms the border of Iran with Turkmenistan; this helped keep the area closed throughout the Cold War years. A 1926 treaty between Iran and Turkmenistan stipulates that Turkmenistan receives approximately 50% of the total Atrek average runoff.
Even though sturgeons concentrate in the area of the Caspian Sea next to the Turkmen coast, they do not currently migrate into the Atrek River owing to its low water level and pollution. Since the Atrek is the only Caspian watershed river of the Turkmen coast, sturgeons no longer reproduce in Turkmenistan.
This river originates from Hezar Masjed and Lalehruban mountains in the province of Khorassan and Golestan and enters the Caspian Sea. Its length is about 600 km.. This river along its course, flows from Shirvan, Bojnurd, Maraveh tappeh and then forms a delta in the south west and enters the Gulf of Hossein Qoli. According to the Iran and Russian agreement in 1882, the Atrak River is a frontier between Iran and Russia after Chat which is now the frontier between Iran and Turkmenistan.