Intensive development of the oil and gas industry and accidents on oil pipelines become the reason of the environmental tension in the Pechora River basin (Nenets Autonomous District). Data on changes in water quality in five lakes and a small watercourse in the territory of oil fields of the Bolshezemelskaya tundra are presented. The bioindication indices (Berger-Parker (D), Shannon biodiversity (H '), Woodiwiss (W), Pantle-Buck (S), Balushkina (Kch)) were applied. The assessment of the state of water bodies in the Kolva River Basin (large lakes - Kolvaty and Nercheity), in the Laya River Basin (shallow lakes - Krugloye, Bezymyannoe 1, Bezymyannoe 2, stream) was done. The 28 samples of zoobenthos was processed by the standard method in July 2012 and 2019. A low diversity of benthic invertebrates was revealed for 5–20 taxa of the rank of families and orders. During the considered period, the changes have occurred in the structure and composition of the zoobenthos of water bodies. In 2019, the species diversity decreased in Kolvaty Lake (H'<2). There are no species of the crustacean complex (Monoporeia affinis, Mesocyclops leuckarti, Heterocope borealis) and larvae of Trichoptera. Only Sphaeriidae and Chironomidae with a predominance of Psectrocladius psilopterus (D = 55%) were recorded. The species diversity in Nercheity Lake increased (H'> 2) with a change in the dominant taxa: the larvae of the chironomids Ablabesmyia monilis (D = 44%) were found in 2012, the lower crustaceans (D = 47–51%) - in 2019. However, according to the totality of hydrobiological indicators, the quality of water in the lakes of the Kolva River Basin in 2019 compared to 2012 did not change significantly. The quality of water in the Krugloye and Bezymyannoe 1, Bezymyannoe 2 lakes (the Laya River Basin) has improved that is confirmed by a significant increase of species diversity. The most characteristic groups of benthic communities in these lakes are lower crustaceans (Cladocera, Copepoda, Ostracoda) and Chironomidae. The indicators of clean waters are o-β-mesosaprobic species Cladocera, Copepoda Heterocope appendiculata, Heterocope borealis (in the oligotrophic lakes), caddisfly Limnephilus stigma (in the Krugloe Lake), rotifer Polyarthra euryptera (in the Bezymyannoe 2 Lake), mayfly larvae Centroptilum luteolum. More resistant to organic pollution Copepoda began to prevail in abundance and diversity in Bezymyannoe 1 and Bezymyannoe 2 lakes, with a decrease in the taxonomic composition of Cladocera, which indicates the eutrophication of these water bodies. In most lakes, the water corresponds to the III quality class ("moderate pollution"), but in the Kolvaty lake and in the Bezymyanny stream (the Laya River basin) was recorded the biogenic pollution. Totally, insignificant taxonomic changes in zoobenthos structure took place in the lakes and the state of water bodies of the surveyed tundra remains relatively stable.
