Why did the salinity of the Aral Sea rise as the lake shrank?

The salinity of the Aral Sea rose significantly as the lake shrank primarily because of the drastic reduction in freshwater inflow from the Amu Darya and Syr Darya rivers.12

Beginning in the 1960s, the Soviet government diverted these rivers for large-scale agricultural irrigation, causing the volume of water reaching the sea to drop sharply. Because the Aral Sea is a closed lake—meaning it lacks an outlet—it relies on river inflow to balance the water lost through evaporation.13

As the rivers were diverted, the lake’s water level fell, and the remaining water was subjected to continuous evaporation. Since evaporation removes only pure water while leaving behind dissolved salts and minerals, the concentration of these substances in the remaining water increased dramatically. This process of intense salinization, compounded by pollution from agricultural chemicals, ultimately destroyed the local fishing industry and created severe environmental and health crises for the surrounding population.132