Abstract
The dynamics of long-term indicators of trophicity in the cooling pond of a nuclear power plant in Ukraine was analyzed by phytoplankton biomass and bioindicators of trophicity. Greater species richness correlated with the number of species-indicators of greater trophicity. During the contourization processes caused by the introduction of filter-feeding mollusks and changes in the operating mode of the nuclear power plant, there was a decrease in the abundance of phytoplankton and trophic state. During decontourization, there was a sequential “return” of previously eliminated taxa and the restoration of the number of indicator species.