Atrek
The Atrek (Persian: اترک, Turkmen: Etrek derýasy), also known as the Attruck,Atrak, and Etrek, is a fast-moving river which begins in the mountains of north-eastern Iran (37°10′N 59°00′E / 37.167°N 59.000°E), and flows 563 kilometres (350 mi) westward draining into the south-eastern corner of the Caspian Sea in Turkmenistan. Because of the high use of its waters for irrigation, it only flows into the Caspian when it is in flood stage.
The Atrek is 669 kilometres (416 mi) long and drains a basin of 27,300 square kilometres (10,500 sq mi).
Beginning at 37°59′28″N 55°16′29″E / 37.99111°N 55.27472°E, where its tributary the Sumbar joins 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 about 50 percent of the total Atrek average runoff.
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