Aral Sea (ărˈəl) [key], salt lake, SW Kazakhstan and NW Uzbekistan, E of the Caspian Sea in an area of interior drainage. To the north and west are the edges of the arid Ustyurt Plateau; the Kyzyl Kum desert stretches to the southeast. As recently as the 1970s it was the world's fourth largest lake, c.26,000 sq mi (67,300 sq km) in area and c.260 mi (420 km) long and c.175 mi (280 km) wide. Fed by the Syr Darya and Amu Darya rivers, it was generally very shallow, attaining a maximum depth of c.180 ft (58 m). In the 1950s the Soviet Union decided to cultivate cotton in the region, and since the early 1960s the Syr Darya and Amu Darya have been used for large-scale irrigation, causing a drop in the flow of freshwater into the sea. The sea is, as a result, now greatly reduced, mainly occupying two basins in the western and northern sections of its former lakebed by 2009, about a tenth of its former size in area.
The sea formerly supported local fishing and was navigable from Muinak to Aral. As the Aral has retreated from its former shores, due to the combined effects of evaporation and water diversion, major environmental problems have resulted. The quality of the remaining water has deteriorated, increased salinity has killed fish, and the health of those living along the shore has suffered. Regional weather has been affected as well, becoming harsher as the sea's moderating climatic influence has diminished. Vozrozhdeniye, the site of a Soviet germ warfare waste dump, is a former island that is no longer isolated from the surrounding region; in 2001 the United States agreed to help clean up the site.
Geologically separate from the Caspian Sea since the last Ice Age, the Aral Sea was once only slightly saline. Mentioned in Arab writings of the 10th cent., it was called the Khwarazm (or Khorezm) Sea by later Arab geographers. It was reached in the 17th cent. by Russians, who called it the Sinyeye More (Blue Sea). The United Nations has estimated that what remains of the sea will essentially disappear by 2020 if nothing is done to reverse its decline. The Kok-Aral Dam (completed 2005) was constructed to enclose the small northern section (in Kazakhstan), which has revived, but it is a fraction of the former sea.