What is "atrek"

The Atrek (, ), also known as the Attruck, Atrak, and Etrek, is a fast-moving river which begins in the mountains of north-eastern Iran , and flows 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.