Proceedings of the International scientific and practical conference ―Science at the Frontier of Civilizations: Challenges and Perspectives‖ (December 27-29, 2025) / Publisher website: www.naukainfo.com. – Helsinki, Finland, 2026. – 252 p.

25 5. Pechenihy Reservoir — the highest proportion of euglenoids and cyanobacteria, low diversity of golden algae; the highest pollution level. Conclusions. In the studied water bodies, species of the β-mesosaprobic zone predominate, indicating a moderate level of organic pollution characteristic of anthropogenically transformed aquatic systems. According to the combined indicators of algal bioindication, Lake Bile is the cleanest water body, with the highest number of oligosaprobic species and a high level of diversity. The most polluted water bodies are the Pechenihy Reservoir and, to a lesser extent, the Seversky Donets River, which is due to intensive anthropogenic pressure and eutrophication. The established sequence of water bodies in increasing order of pollution is: Lake Bile → Pioneer Pond → Haidarivskyi Pond → Seversky Donets River → Pechenihy Reservoir. The obtained results confirm the effectiveness of using algae as bioindicators and emphasize the need for further monitoring of regional water bodies, taking into account the dynamics of algal flora. REFERENCES: 1. Xue H., Li X., Wang Y., et al. Exploration of applicability of diatom indices to evaluate water quality in a river basin. Water, 2023, 15(20), 3695. 2. Tekebayeva Z., et al. Ecological assessment of phytoplankton diversity and water quality in freshwater ecosystems. Sustainability, 2024, 16(22), 9628. 3. Hui H., et al. Ecological assessment of water quality in freshwater wetlands using phytoplankton community structure. PLOS ONE, 2024. 4. Jasim H. A. Diatom indices for assessment of the water quality. Egyptian Journal of Aquatic Biology and Fisheries, 2024. 5. Hasrini D. A. Epipelic diatoms to determine ecological status based on trophic/diatom indices, 2023.