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During the latter half of the twentieth century , the desiccation of the Aral Sea became an emblem of anthropogenic environmental collapse . Once the fourth - largest inland water body on Earth , this terminal lake contracted precipitously after Soviet central planners diverted its two primary tributaries , the Amu Darya and the Syr Darya , to irrigate intensive cotton monocultures . This diversion starved the closed basin of its historical inflow , precipitating an ecological crisis of unprecedented scale . As water levels plummeted , the retreating shoreline exposed millions of hectares of hyper - saline seabed . Toxic dust storms laden with agricultural residues subsequently degraded ambient air quality and public health across Central Asia , while the regional commercial fishing industry ceased entirely . By the late 1980s , the shrinking lake had fragmented into distinct hydrological zones , separating the northern Small Aral from the larger southern depression . Recognizing that restoring the entire expanse exceeded regional water budgets , the government of Kazakhstan collaborated with the World Bank to implement an engineering intervention . Their strategy focused exclusively on conserving the northern basin . In 2005 , engineers completed the Kokaral Dam , a thirteen - kilometre earthen dike spanning the Berg Strait . Equipped with an adjustable concrete spillway , this barrier captured the remaining seasonal discharge of the Syr Darya , preventing freshwater from dissipating into the desiccated southern depression . The hydrological response to this barrier surpassed initial scientific forecasts . Within eight months of completion , water levels in the North Aral rose from thirty to thirty - eight metres above sea level , a recovery that hydrologists had projected would require several years . As the northern reservoir expanded by nearly twenty percent , salinity dropped from exceeding thirty grams per litre to under ten grams per litre in major sectors . This dilution permitted the resurgence of native and introduced freshwater fauna , most notably the pikeperch and carp . Consequently , artisanal fishing fleets resumed commercial operations , revitalizing economic life in peripheral settlements such as Aralsk , which had been stranded far inland . Nevertheless , this regional success highlights a difficult environmental trade - off . Retaining the Syr Darya in the north curtailed residual flows to the southern basin , accelerating the eventual desiccation of the South Aral Sea into an arid salt desert known as the Aralkum . How should environmental managers weigh the revitalization of one micro - basin against the permanent loss of an adjacent ecosystem ? Could such selective engineering interventions be applied to other distressed terminal lakes in your country , and what long - term monitoring would you require before approving similar hydraulic projects ?
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