The Atrek is a fast-moving river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 which begins in the mountains of Northeastern Iran

Iran

Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

 (37°10′N 59°00′E), and flows 563 km (349.8 mi) westward draining into the southeastern corner of the Caspian Sea

Caspian Sea

The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...

 in Turkmenistan

Turkmenistan

Turkmenistan , formerly also known as Turkmenia is one of the Turkic states in Central Asia. Until 1991, it was a constituent republic of the Soviet Union, the Turkmen Soviet Socialist Republic . Turkmenistan is one of the six independent Turkic states...

. Because of the high use of its waters for irrigation, it only flows into the Caspian when it is in flood stage.

Politics

Beginning at 37°59′28"N 55°16′29"E, where its tributary the Sumbar

Sumbar River

The Sumbar is a fast flowing river in southern Turkmenistan and northern Iran. It a tributary of the Atrek. The name Sari-su means yellow water in Turkic languages, but is applied to a number of other rivers as well.-Geography:The Sumbar is 245 km long and drains a basin of 8300 km²...

 join it, the river forms the border of Iran with Turkmenistan

Turkmenistan

Turkmenistan , formerly also known as Turkmenia is one of the Turkic states in Central Asia. Until 1991, it was a constituent republic of the Soviet Union, the Turkmen Soviet Socialist Republic . Turkmenistan is one of the six independent Turkic states...

; this helped keep the area closed throughout the Cold War

Cold War

The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...

 years. A 1926 treaty between Iran

Iran

Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

 and Turkmenistan stipulates that Turkmenistan receives approximately 50% of the total Atrek average runoff.

Ecology

Even though sturgeon

Sturgeon

Sturgeon is the common name used for some 26 species of fish in the family Acipenseridae, including the genera Acipenser, Huso, Scaphirhynchus and Pseudoscaphirhynchus. The term includes over 20 species commonly referred to as sturgeon and several closely related species that have distinct common...

s 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.