The International Lake Environment Committee (ILEC) has been conducting, in cooperation with the United Nations Environment Programme (UNEP), a project entitled the “Survey of the State of World Lakes” since 1986 with the aim of collecting and compiling environmental data on as many important lakes and reservoirs of the world as possible to be used as the basis for environmentally sound management of lakes. The results so far obtained from the survey have been published in five volumes as the “Data Book of World Lake Environments”, which contain sets of detailed data on 217 lakes from 73 countries all over the world. The survey carried out by ILEC and UNEP illustrated that the following six major environmental problems are now widespread among lakes and reservoirs around the world, leading to a crisis of water resources and aquatic ecosystems: 1) Lowering of water level, 2) Rapid siltation, 3) Acidification, 4) Toxic contamination, 5) Eutrophication, and 6) Extermination of ecosystems and biota. A preliminary analysis on surveyed lakes and reservoirs also demonstrated some interesting correlations between 1) the volume of lake water and transparency, 2) suspended solids concentrations and the ratio of forest area to the whole catchment area, 3) suspended solids concentrations and the area of farmlands in the catchment area per unit volume of lake water, and 4) total nitrogen and total phosphorus concentrations in lake water, indicators of the degree of eutrophication, and the catchment area population per unit volume of lake water.

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