World's largest inland sea, on the border between Europe and Asia east of the Black Sea, divided between Iran, Azerbaijan, Russia, Kazakhstan, and Turkmenistan. It extends north–south for 1,200 km/745 mi, and its average width is 300 km/186 mi; area about 400,000 sq km/155,000 sq mi, with a maximum depth of 1,000 m/3,250 ft. An underwater ridge divides it into two halves, of which the shallow northern half is almost salt-free. There are no tides, but violent storms make navigation hazardous. The chief ports are Astrakhan (Russia), Baku (Azerbaijan), and Bandar Shah (Iran). The River Volga supplies 80% of freshwater inflow; the Ural, Emba, Terek, Kura, and Atrek rivers also flow into the Caspian Sea. Prolonged drought, drainage in the north, and regulation of the Volga and Kura rivers reduced the area from 430,000 sq km/166,000 sq mi in 1930 to 382,000 sq km/147,000 sq mi in 1957, and left the sea approximately 28 m/90 ft below sea level. This turned much of the shallow northeastern part of the sea into dry land or marsh. In June 1991 opening of sluices in river dams caused the water level to rise dramatically to its former level, threatening towns and industrial areas.
Falling water levels have had an adverse effect on fish numbers, particularly salmon and sturgeon, on which caviar and isinglass industries are based. In addition, the growth of industry has caused pollution and damaged Russian and Iranian caviar production. Some 40% of Russia's polluted waste water flows into the sea.
On the east of the sea is the Zaliv Kara-Bogaz Gol basin. In 1980 the basin was separated from the sea by a dyke to stop water flowing into the basin and thus reducing the lowering of the water level in the main sea. In 1992 part of this damming scheme was demolished in an attempt to alleviate the environmental damage it had caused.
The Caspian Sea is exploited for its oil and gas deposits. A major pipeline runs from Azerbaijan through Russia. In the 1990s other pipeline routes were being considered. The area has the world's largest deposits of sulphate.
The sea is linked with the Baltic, Black, and White seas by means of canal systems and the Volga River.
In prehistoric times, the present sea probably extended as far as the Arctic Ocean, and was united with the Black Sea in the west. More recently the Caspian and Aral seas constituted a single sea, evidenced by the high-level terraces (former beaches) which surround part of the Caspian shoreline.
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