1. Limnological changes to the Aral Sea, a large saline lake in central Asia, are considered. Important changes include the decreased water-level (c. 15 m), the recession of the shoreline (up to 120 km in places), the exposure of large areas of lake bed, the increased salinity (from c. 10 to 30 g 1−1), and the marked alteration in the nature of the lacustrine biota involving decreases in diversity and biomass and the introduction of species.
2. Fish have virtually disappeared from the lake and the diversity of associated bird and wildlife communities has decreased.
3. The major cause of the limnological changes is the diversion of water, mainly for agricultural purposes, from inflowing rivers (the Amu- and Syr-Darya), and, to a lesser degree, species introductions.
4. Limnological changes have been accompanied by changes to regional rivers and terrestrial environments, groundwaters, climate, and to agricultural productivity.
5. It is concluded that four major values of the lake (economic, cultural, scientific, and environmental) have been seriously diminished by recent changes to it. The need to continue limnological studies is stressed.