The greatest world reservoir of fresh water, the unique Lake Baikal, is at risk from anthropogenic influence. Three stages of economic activity in the lake region can be distinguished: (i) poor economic uses, (ii) increase of economic uses after the construction of the hydropower station dam on the outflow of the lake, and (iii) intensive increase of economic activity, characterized by the intensive use of mineral fertilizers, transportation, log rafting, growth of population around Baikal, mass development of tourism, the construction of the Baikal-Amur railroad and pulp combines. Chemical and biological pollution of the lake, fishing and hunting, the state of coasts and protected areas are discussed. The regions most affected are listed. The greater long-term influence is an increase in the mineralization of tributary waters due to forest cutting and land cultivation. Though the influence does not cause a decline in water quality, the properties of the Baikalian water in local sites of pollution can significantly differ from their initial state. The quality of water, however, is within the limits of requirements for fresh drinking water,

Lake Khubsugul phytoplankton is dominated by Diatoms and Chlorococcales . Its algal flora is rather peculiar, but lacks Baikalian endemics.Primary production ranges from 2 to 5 mg C m -3 d -1 . Total bacteria in the open water is 150-200 x 10 3 cells ml -1 .Predominant in numbers and biomass throughout the year are two pelagial species of Copepoda -the endemic Mixodiaptomus kozhoŢi Step ., and Cyclops abyssorum Sars .The bottom fauna consists of cold stenothermic inŢertebrates, mostly Chironomidae . In biomass, they rank only third, howeŢer, after Gammaridae and Mollusca . The aŢerage zoobenthos biomass of the lake is 5 .5 g m -2 .

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Elodea canadensis Michx. was first observed in Lake Baikal at the end of the 70's.E. canadensis was probably introduced to Baikal by aquarists or by transport vehicles and transport together with fishes taken from lakes of the Urals, where mass development of the plant was observed at the beginning of the present century. The spread of E. canadensis along lake Baikal may be due to navigation, but natural factors also affect its spread.The fast spread of E. canadensis, its high competitive quality and metabolic properties for purifying sewage waters are of interest.The expansion of E. canadensis may be considered a catastrophic phenomenon; its effect now covers practically the whole perimeter of Lake Baikal.

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