Between 1967 and 1997, the Aral Sea, once at 65,000 square kilometers the world's fourth-largest lake, has shrunk by more than half, to 12,000 miles. For thousands of years Central Asia's two great rivers, the Amy Darya and the Syr Darya, fed the Aral. But as this region became the main Soviet source of cotton, a maze of irrigation canals was built. Much of the diverted water was lost to evaporation and seepage, because the canals were neither covered nor lined. After those losses and the huge amounts of water that the cotton plantations absorbed, only a trickle was left to feed the Aral.