 Biodiversity of fish fauna was considerably increased over the first 15 or 20 years following construction of the tandem reservoir system, and some species gained importance as a fishery.Increasing salinity decreased fish yields in Proletarskoe reservoir, and fishing is possible only in mouths of rivers entering reservoirs.Biodiversity of fish fauna and its productivity might be improved by construction of the canal to supply Mancy-Gudilo Lake with fresh water to reduce salinity.