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The research assesses the state of different types of lakes in specially protected natural areas of the Nizhny Novgorod Region and the anthropogenically disturbed territory of Nizhny Novgorod. The trophic status of water bodies was determined using the trophic status index ( TSISD ). It has been established that most of the lakes have eutrophic and mesotrophic status. The analysis of the species structure of zooplankton in water bodies has been carried out. The species richness of both lakes of the protected areas and urban lakes was high. Along with eurybiontic species, alien and rare species of zooplankton were identified. Significant differences in the indicators of the species structure were established, however, no critical values of the abundance, biomass, Shannon and Pielou indices were recorded. Most of the identified zooplankton species were indicative. On the basis of the Pantle-Bukk saprobity index in the Sladecek modification, the water quality class was established. The reservoirs were characterized by quality class II-III (clean-moderately polluted water). In some lakes an excess of the maximum permissible concentrations of ammonium, nitrite, iron, manganese, copper, zinc, lead has been established. However, in general, in terms of a set of indicators, water bodies are in a satisfactory condition. In order to objectively assess the ecological state of aquatic communities, to predict possible changes and develop recommendations for the conservation of species diversity, it is important to carry out regular monitoring studies.

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The paper presents the results of zooplankton research in June, July and September 2017 in eight floodplain lakes of the middle reaches of the Kerzhenets River located in the Kerzhinski Nature Reserve. The studied water bodies are shallow lakes with weakly acidic pH (5,40-6,23) and low mineralized water (46,90-68,40 mg/l), with increased chromaticity (202,00-1048,20 deg.) and content of suspended substances (4,40-22,90 mg/l). As a result of a carried out hydrobiological research, 106 species of zooplankton were identified. According to the zoogeographical characteristics, the zooplankton fauna of floodplain water bodies is typical for the European part of Russia, with the exception of two invasive species: the North American rotifers Kellicottia bostoniensis (Rousselet, 1908) and the Caspian branching diocese of southern origin Diaphanosoma orghidani (Negrea, 1982). In addition, in a number of lakes, the Arctic relict crustacean Holopedium gibberum (Zaddach, 1855) was found. The crustacean is listed in the Red Data Book of the Nizhny Novgorod Region. Alien rotifers in a number of floodplain reservoirs were the dominant species and had a high abundance. The Caspian southern crustacean was found only in two reservoirs, its number was not high, and it did not play a significant role in the zooplankton communities of these reservoirs. New findings of the Arctic relict species Holopedium gibberum (Zaddach, 1855) make it possible to recommend the introduction of a number of floodplain reservoirs into the Red Book of the Nizhni Novgorod Region as habitats of this rare species. Statistical redundancy analysis (RDA) has revealed four factors that related with development of zooplankton in a number of floodplains, such as water temperature, hydrogen index, dissolved oxygen content and suspended solids.