The Aral “Sea,” lying between Kazakhstan and Uzbekistan was once a large saltwater lake that covered some 26,300 square miles (68,000 square km) and was the fourth largest inland body of water in the world. But, in the last 50 years, as the waters of the Syr Darya and Amu Darya rivers were diverted for irrigation purposes, the lake has almost totally dried up, increasing salinity and spreading toxic substances on the now exposed soil.

This interactive, created by Britannica cartographer Ken Chmielewski, shows the the scale of the decline of the lake. (If the image does not appear, you will need to download a Flash Player here or click here to view the interactive on Britannica’s Web site.)

John Rafferty, Britannica’s earth sciences editor, relates the demise of the Aral Sea to the broader debate over human impact on the environment.

One of the leading arguments against spending money on environmental issues is the contention that humans couldn’t possibly change Earth because the planet, its atmosphere, and its oceans are so vast. The draining of the Aral Sea is stark evidence that humans influence the biosphere at global scales.

Sometimes the pictures of this “sea” are unimaginable, as in this image below of a ship abandoned in the middle of what used to be the lake.

Area once covered by the Aral Sea in Kazakhstan; photo credit: P. Christopher Staecker

Shipwrecks at "Sheep's Cemetery" in the Aral Sea, 2005; photo credit: Vyacheslav Oseledko—AFP/Getty Images

For further imagery, see photographs from National Geographic and satellite shots from NASA.

As Britannica describes, the environmental and health costs have been enormous. Vorozhdenya, an island in the Aral Sea, had once been a testing ground for Soviet biological weapons in the Cold War:

In addition to testing done there on such agents as tularemia and bubonic plague, hundreds of tons of live anthrax bacteria were buried on the island in the 1980s. In 1999 still-living anthrax spores were discovered on the site, and scientists feared that when the island was no longer surrounded by water, land vertebrates could carry anthrax to populated areas.

The health costs to people living in the area had already begun to emerge. Hardest hit were the Karakalpaks, who live in the southern portion of the region. Exposed seabeds led to dust storms that blew across the region, carrying a toxic dust contaminated with salt, fertilizer, and pesticides. As a result, health problems occur at unusually high rates—from throat cancers to anemia and kidney diseases—and infant mortality in the region is among the highest in the world.