The correlation between the dynamics of quantitative and qualitative indicators of zooplankton cenosis in the Middle Daugava River and changes in environmental factors was examined. It was found that changes in the abundance, biomass and taxa of zooplankton were significantly affected by thermal conditions, hydrological regime, chlorophyll-a and phosphates. The possible role of environmental factors (lucidity, dissolved oxygen, conductivity, pH, oxidation reduction potential, nitrate, chemical oxygen demand) in controlling dynamics of the Daugava River zooplankton is indicated.