Formerly one of the four largest lakes in the world with an area of 68,000 km2 (26,300 sq mi), the Aral Sea has been steadily shrinking since the 1960s after the rivers that fed it were diverted by Soviet irrigation projects.
Source: http://en.wikipedia.org/wiki/Aral_Sea706px-Aral_Sea_1989-2008

Aral Sea – 1960 and 2007 – Irrigation fail