Caspian Sea (ancient Caspium Mare or Hyrcanium Mare), saltwater lake in southeastern Europe and southwestern Asia, the largest inland body of water in the world. The Caspian Sea is bordered on the west by Azerbaijan and Russia, on the northeast and east by Kazakhstan, on the east by Turkmenistan, and on the south by Iran. It extends about 1210 km (about 750 mi) in a northern and southern direction and about 210 to 436 km (about 130 to 271 mi) in an eastern and western direction. It has an area of 371,000 sq km (143,000 sq mi). The Caspian coastline is irregular, with large gulfs on the east, including Krasnovodsk Gulf and the very shallow Garabogazköl Gulf, which acts as an evaporation basin and is the site of a major chemical plant that extracts salts from the deposits.
The Caspian Sea has a mean depth of about 170 m (about 550 ft) and is deepest in the south. Its level varies from year to year but averages about 28 m (92 ft) below sea level. In the 1960s and 1970s the level fell substantially, partly because water was withdrawn from tributary rivers for irrigation and other purposes. In 1980 a dike was built across the mouth of Garabogazköl Gulf in northwestern Turkmenistan to reduce water loss, creating a lake that was expected to last for several years. Instead, the gulf dried up completely by 1983. In the meantime, the level of the Caspian Sea began rising again at a rate of about 14 to 20 cm (about 6 to 8 in) annually.
The southern and southwestern shorelines of the Caspian Sea are bordered by the Elburz Mountains and the Caucasus Mountains. The sea has numerous tributaries, notably the Volga, Ural, and Zhem rivers, all of which flow into it from the north. Other tributaries include the Gorgan (Gurgan) and Atrek rivers, flowing from the east, and the Kura River, flowing from the west. The Caspian Sea has no outlet. However, it is linked to the Baltic Sea, the White Sea, and the Black Sea by an extensive network of inland waterways, chief of which is the Volga River.
Navigation is frequently dangerous because of violent southeastern storms. During the winter months the northern parts of the Caspian Sea are closed by ice. The chief ports are Krasnovodsk, Turkmenistan; Baku, Azerbaijan; and Makhachkala, Russia.
The Caspian Sea region contains significant reserves of oil and natural gas. The region is estimated to hold the third largest reserves after the Middle East and Russia. Bordering countries are actively exploring and tapping offshore reserves. However, national rights to offshore oil and gas fields have been a point of dispute. In May 2003 Russia, Azerbaijan, and Kazakhstan signed an agreement establishing boundaries in the Caspian Sea, dividing the northern 64 percent of the seabed into national sectors and allowing the surface to be used in common. Iran and Turkmenistan refused to sign the agreement and continue to dispute offshore boundaries. Azerbaijan and Kazakhstan are the region’s leading oil exporters. Baku, the capital of Azerbaijan, is the chief point of export for oil obtained from offshore fields. A new oil pipeline linking Baku with the Mediterranean seaport of Ceyhan, Turkey, opened in 2005, supplementing two other pipelines linking Baku to ports on the Black Sea.
Decades of environmental mismanagement have led to severe pollution problems in the Caspian region. Discharges from offshore oil and gas drilling and inflows from the highly polluted Volga River have contributed to the degradation of Caspian waters. The pollution poses a serious threat to animal life, including tortoises, porpoises, and seals. In addition, overfishing has depleted the sea’s stocks of sturgeon (a source of caviar), salmon, perch, herring, and carp. In November 2003 representatives from all the bordering countries signed the United Nations-sponsored Convention for the Protection of the Marine Environment of the Caspian Sea, which provided a framework for alleviating environmental damage in the region. However, environmental laws and regulations remain weak. See also Fisheries.