The changes in the various components of the water balance of the Aral Sea, since 1960, and the consequent effects on salinity, surface area and water levels, are described. Since 1989 the fall in level has divided the Aral Sea into two parts, a northern Small Aral Sea and a southern Large Sea. The Small Sea receives part of the inflow of the Syrdar'ya and since 1990 its level has risen and its salinity has declined. To prevent the Small Sea overflowing into the south, a dam was constructed. Although this soon failed, the fauna and flora has begun to recover to some extent in the north Aral Sea. The desirability of a scientific and engineering programme to rehabilitate the northern sea is discussed.