Relevance. New units commissioning at the operating nuclear power plants may be associated with an increase in the radiation load on environment and human beings. The 4th Unit BN-800 was commissioned at the Beloyarsk nuclear power plant (BNPP) in 2016. The Beloyarsk artificial lake created in 1959–1963 serves as a cooling pond. A radioecological study of the cooling pond was performed in 2014 before the BN-800 Unit commissioning. Its results were published in the issue No. 2 of the present

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... al in 2016.Intention. The objective of the work is to show (comparing with the results of the previous research) the effect of the BN-800 Unit commissioning on the cooling pond radioecological state.Methodology. The samples of water and macrophytes (Potamogeton pectinatus, Ceratophyllum demersum, Spirogyra, Cladophora) were examined at the reference points of the cooling pond.Results and Discussion. It was found that 137Cs decreased in the water by 1.4–5.9 times in all reference points (including the 4th NPP Unit discharge channel) compared to 2014. Potamogeton pectinatus (from the 4th NPP Unit discharge channel) had 3.1 times less 137Cs and 1.4 times less 90Sr than macrophytes from the Pyshma river area below the dam.Conclusion. The BN-800 Unit commissioning was not associated with additional radiation load on the artificial lake. It does not deleteriously affect the natural purification processes after the 1st and 2nd BNPP Units decommissioning. The further preservation of the Beloyarsk artificial lake natural resources assumes a systematic radioecological monitoring to determine the level of long-lived radionuclides in main natural components of the cooling pond.Sampling from the cooling pond, sample preparation, 137Cs and 90Sr concentration measurement in water and aquatic plants as well as interpretation of results are performed in the framework of the State Task of the Institute of Plant and Animal Ecology, Ural Branch of the Russian Academy of Sciences.