Which sea did the Soviet irrigation of two rivers reduce to a tenth of its volume?

The Aral Sea. It was the fourth-largest lake on Earth; from the 1960s the Amu Darya and Syr Darya were diverted to irrigate cotton in the desert, and it has lost around 90 per cent of its volume. Fishing towns now sit fifty or more kilometres from any water, with rusting trawlers on sand.

It was not an accident. Soviet planners calculated that the sea would shrink and decided the cotton was worth more - one hydrologist wrote that its evaporation was pointless and its disappearance inevitable. What they did not price was the exposed lakebed: tens of thousands of square kilometres of salt and agricultural chemicals lifted by the wind into dust storms, with local rates of respiratory disease, kidney disease and infant mortality rising accordingly.

The seabed also gave up a secret. Vozrozhdeniya Island held a Soviet biological weapons test site, and as the water fell it stopped being an island and became connected to the mainland - which meant securing buried anthrax spores became urgent. Kazakhstan has since dammed and partly refilled the small northern lobe, where the fish came back; the much larger southern part, in Uzbekistan, is written off.