SUMMARYDue to water withdrawal for land irrigation purposes, the Aral sea was definitively separated into two lakes, the Small and Large Aral, in the late 1980s. Since then, both lakes have followed their own hydrobiological evolution. The Large Aral is continuously drying out at a rate of around 80 cm/year, and is now at a level 10 m below the Small Aral, in the north. We discuss the evolution of the Small Aral during the 1990s in terms of hydrological water mass balance and consequences on hydrobiology. A satellite altimetry technique has been used to monitor the variation of the Small Aral sea level every ten days from 1993 up to 2003. During the same period various in-situ data have been collected: salinity of the sea, runoff of the Syr Darya, evaporation and precipitation over the lake, and biological parameters related to phytoplankton, zooplankton and zoobenthos. During this period a dam in the Berg's strait has been built and the flow of the Syr Darya has been artificially channelled in order to retain the water from the Syr Darya river inside the Small Aral sea. This dam was not sufficiently resistant to water pressure and was destroyed many times. However, it led to a significant increase of the level of the Small Aral, and a decrease in salinity, and thus has had a significant effect on biomass and bio-productivity, and hence on fishery activities. The short period when the dam was installed has demonstrated the positive influence on future possible restoration and rehabilitation of the marine ecosystem in the Small Aral.

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There are > 3500 lakes of area > 0.1 km2 in Mongolia. Most have salinities > 1 g l-'. Of these saline lakes, 12 have areas > 50 km2 each, 10, areas > 100 km2, and 2, areas r 1000 km2. Limnological investigations of salt lakes include morphometric studies, and investigations of bottom sediments, thermal regimes, chemical features, and biological (including fish) characteristics. Data from these investigations now provide a much clearer picture of the limnology of saline lakes in central Asia.