Rivers Running Dry

Some of the world's most important rivers no longer reach the sea. The Colorado River supplies water to roughly 40 million people across seven US states and Mexico, yet so much is drawn off that its delta is mostly dry dust.

Its two giant reservoirs, Lake Mead and Lake Powell, have fallen to their lowest levels since they were first filled.

The Aral Sea was once the world's fourth-largest lake. Then the Soviet Union diverted the two rivers feeding it to water cotton fields, and the sea lost about 90% of its volume.

Fishing boats now rust on sand more than 100 kilometers from any water. The bare seabed turned to dust, and storms carry its salt and old pesticide residue across Central Asia.