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 northeastern Iran (37°10′N59°00′E), and flows 563 kilometres (350 mi) westward draining into the southeastern corner of the Caspian Sea in Turkmenistan.