The Aral Sea, which lies between Uzbekistan and Kazakhstan, was once the fourth largest lake in the world. It hasn't been doing too well of late, largely as a result of persistent governmental tinkering dating back to the Soviets, as Wikipedia explains:
By 1960, somewhere between 20 and 50 cubic kilometers of water were going each year to the land instead of the sea. Thus, most of the sea's water supply had been diverted, and in the 1960s the Aral Sea began to shrink. From 1961 to 1970, the Aral's sea level fell at an average of 20 cm a year; in the 1970s, the average rate nearly tripled to 50–60 cm per year, and by the 1980s it continued to drop, now with a mean of 80–90 cm each year. After seeing this, the rate of water usage for irrigation continued to increase: the amount of water taken from the rivers doubled between 1960 and 1980; cotton production nearly doubled in the same period. The disappearance of the lake was no surprise to the Soviets; they expected it to happen long before. The Soviet Union apparently considered the Aral to be "nature's error", and a Soviet engineer said in 1968 that "it is obvious to everyone that the evaporation of the Aral Sea is inevitable". . .
