The Aral Sea is the fourth largest lake in the world

What actually happened

Soviet planners diverted the Amu Darya and Syr Darya rivers in the 1960s to irrigate cotton in the desert. The rivers fed the Aral Sea; the sea began to shrink almost immediately, and by the 1990s it had split into separate bodies. NASA's satellite time series of the collapse is one of the most-viewed images in environmental science.

The consequences kept compounding. The exposed seabed, laced with salt and agricultural chemicals, became a source of toxic dust storms; the fishing industry that employed 40,000 people collapsed; local climate shifted toward harsher extremes as the moderating water disappeared. Kazakhstan built the Kok-Aral dam in 2005 to save the northern portion, and that section has partially recovered, with fish returning. The large southern basin is essentially gone. This entry is here as the clearest case on the site of a geography fact that changed not because our knowledge improved, but because the thing itself was destroyed within one lifetime.