Talk about a sea change: From 2006 (bottom) to 2009, Central Asia's vast Aral Sea dramatically retreated, with its eastern section losing about 80 percent of its water in just four years. The sea level of this already-shallow lake dropped about 16 meters (52.5 feet), while its shoreline receded up to 120 kilometers (75 miles).

The immense body of water, which straddles Uzbekistan and Kazakhstan, was once the world's fourth-largest lake. But in the past 30 years, 60 percent of the lake and the Amu Darya (the river that traditionally feeds the lake) have been diverted to irrigate cotton crops, according to NASA's Earth Observatory.

The Aral Sea was always a saline lake, but it has become much saltier as its waters have receded. In some places in the eastern seabed, salt flats spread for more than 100 kilometers (62 miles). Winds pick up the salt and deposit it over agricultural lands, spoiling some of the fertilized, irrigated soil. More than 40 million metric tons of dried salt have been swept into agricultural lands.

This satellite imagery, from the European Space Agency, dramatically illustrates the Aral Sea's disappearance. With little government attention, it's likely that at least part of the sea may be gone for good, experts say.

Noun

the art and science of cultivating the land for growing crops (farming) or raising livestock (ranching).

Noun

agricultural produce.

divert
Verb

to direct away from a familiar path.

government
Noun

system or order of a nation, state, or other political unit.

irrigate
Verb

to water.

Noun

body of water surrounded by land.

NASA
Noun

(National Aeronautics and Space Administration) the U.S. space agency, whose mission statement is "To reach for new heights and reveal the unknown so that what we do and learn will benefit all humankind."

recede
Verb

to retreat or withdraw.

Noun

large stream of flowing fresh water.

saline
Adjective

salty.

salt flat
Noun

large, flat expanse of earth covered by a thick layer of salt left by an evaporated saline lake or pond. Also called a playa, sink, or salt pan.

satellite imagery
Noun

photographs of a planet taken by or from a satellite.

Noun

large part of the ocean enclosed or partly enclosed by land.

Noun

base level for measuring elevations. Sea level is determined by measurements taken over a 19-year cycle.

shore
Noun

coast.