Formerly the fourth-largest lake in the world with an area of 68,000 km2 (26,300 sq mi), the Aral Sea has been shrinking since the 1960s after the rivers that fed it were diverted by Soviet irrigation projects. By 1997, it had declined to 10% of its original size, splitting into four lakes – the North Aral Sea, the eastern and western basins of the once far larger South Aral Sea, and one smaller intermediate lake. By 2009, the southeastern lake had disappeared and the southwestern lake had retreated to a thin strip at the western edge of the former southern sea; in subsequent years, occasional water flows have led to the southeastern lake sometimes being replenished to a small degree. Satellite images taken by NASA in August 2014 revealed that for the first time in modern history the eastern basin of the Aral Sea had completely dried up. The eastern basin is now called the Aralkum Desert.
In an ongoing effort in Kazakhstan to save and replenish the North Aral Sea, a dam project was completed in 2005; in 2008, the water level in this lake had risen by 12 m (39 ft) compared to 2003. Salinity has dropped, and fish are again found in sufficient numbers for some fishing to be viable. The maximum depth of the North Aral Sea is 42 m (138 ft) (as of 2008).
The shrinking of the Aral Sea has been called "one of the planet's worst environmental disasters". The region's once-prosperous fishing industry has been essentially destroyed, bringing unemployment and economic hardship. The water from the diverted Syr Darya river is used to irrigate about two million hectares (5,000,000 acres) of farmland in the Ferghana Valley. The Aral Sea region is also heavily polluted, with consequential serious public health problems.
UNESCO added the historical documents concerning the development of the Aral Sea to its Memory of the World Register as a unique resource to study this "environmental tragedy".