Lake Balkhash is one of the many closed lakes in Central Asia. Mechanisms of demineralization in Lake Balkhash were considered from results of surveys undertaken on the lake and along the Ili River. Electrical conductivity (EC) values at the eastern coast in south-western Lake Balkhash were higher than those of the western coast. The Ili River enters at the south-western corner of the lake, so that EC values of this area are low. This water flows westwards. The distribution of Ca2+ concentrations showed that these were lower value in Lake Balkhash than along the Ili River, implying Ca2+ removal by the lake. Amongst suspended mineral matter in the lake occur calcite and dolomite. Thus, a possible mechanism of calcium removal is that it is removed as crystals of calcite or dolomite. SO42- concentration within the lake has increased for the past 37 years. This may be caused by the discharge into the lake from the city of Balkhash of waste water from a copper smelter.