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.

23 Purpose of the study. The aim of the study was to assess the ecological status of water bodies in the Seversky Donets River basin based on the analysis of algal species that serve as indicators of water saprobity. To achieve this aim, the following tasks were performed: 1. Sampling from all major ecological groups of algal flora: plankton, benthos, and periphyton. 2. Identification of the taxonomic affiliation of the detected algae. 3. Analysis of species composition from the standpoint of indicator value and assignment to specific saprobity zones. 4. Comparison of saprobity levels among different water bodies of the Seversky Donets basin. The object of the study was the ecological status of water, and the subject was the species composition of saprobity indicator algae. Presentation of the main material. Material collection was carried out according to generally accepted hydrobiological methods. Plankton samples were obtained by filtering 50–100 liters of water through a plankton net. Benthic algae were collected using a spoon and a Perfiliev device by sampling bottom sediments from the coastal zone. Periphyton was scraped from the surfaces of stones, plants, and artificial substrates. All samples were fixed with a 4% formalin solution and transported to the laboratory for further analysis. Species identification was carried out using a binocular microscope in accordance with freshwater algae identification guides. The ecological status was assessed based on the quantitative ratio of species belonging to specific saprobity zones. The study covered the following water bodies: Lake Bile, Pioneer Pond, Haidarivskyi Pond, the Seversky Donets River, and the Pechenihy Reservoir. General characteristics of algal flora. In the water bodies of the Seversky Donets basin, representatives of the main divisions of freshwater algae were identified: Bacillariophyta (diatoms) — dominant in river ecosystems; Chlorophyta (green algae) — typical of stagnant water bodies; Euglenophyta (euglenoids) — indicators