Declining water levels
Falling water levels and the resulting shrinkage of lake areas are
due to the overuse of water drawn from the lake itself or from inflowing or
The extreme case of the Aral Sea is now widely known. Similar
situations are also reported for other Central Asian lakes such as the Caspian
Sea in the middle decades of the twentieth century (Golubev, 1992), Lake
Balkhash in Kazakhstan, Lake Qinghai in China, and some lakes in Iran. Lake Mono
in California also lost about 30 per cent of its former area owing to a fall in
the water level of 11 m, and suffers from raised salt concentration in the lake
water (as does the Aral Sea), owing to the diversion of 85 per cent of its
tributary river water to the city of Los Angeles.
Aside from such lakes in the arid zone, the water level in other
lakes has often been significantly lowered by dredging their outlets in order to
increase the capacity of hydroelectric power generation in outflowing rivers.
This has often caused the temporary advance of eutrophication, as, for instance,
was the case in Lake Sevan Armenia (Oganesian, 1991).
Fig. 3.1 The transparency of lake
water in relation to lake water volume in 145 lakes and reservoirs of the
Fig 3.2 Six major environmental
problems of world lakes and