The Caspian Sea is a blue plain bounded from the south to Iran, from the north to Russia, from the west to Russia and Azerbaijan, and from the east to the republics of Turkmenistan and Kazakhstan. The Caspian Sea was formerly part of the Tethys Sea connecting the Pacific to the Atlantic Ocean.
This sea which sometimes classified as the largest lake in the world, and sometimes the smallest self-sufficient sea of the planet, is the largest enclosed water zone. Its length is about 1030 to 1200 kilometers and its width is between 196 and 435 kilometers. The Caspian Sea level is lower than the free seas.
The northern part of this sea is very shallow. So that only half a percent of the seawater is located on the northern quarter of the sea and its depth average is less than 5 meters. About 130 rivers flow into this sea, most of them come from the northwest of the sea. The largest is the Volga River, which annually pours 241 cubic kilometers of water into the Caspian Sea. The rivers Kura, Atrak, Ural and Sulak pours respectively 13, 8.5, 8.1 and 4 kilometers of cubic meters of water to the sea annually.
The nature of the Caspian Sea has made it a unique place for animals and plants, but at the same time has made it vulnerable to agricultural, industrial and oil pollution. Of the important sources of the Caspian Sea, the oil and gas reserves available under the sea bed, as well as sturgeon species, can be mentioned.
The level of the Caspian Sea is lower than the international waters, and now it is (from the beginning of the twenty-first century), 26, 5 to 28 meters below sea level. The coastline of the sea is about 7,000 kilometers, its area is 371 to 386 thousand square kilometers (one and a half times the size of the Persian Gulf) and its volume of water is 78700 cubic kilometers.