Abstract: Longgan Lake, located in the Huayang River and Lake Group Nature Reserve in Anhui Province, boasts significant ecological value. Scientific assessment of the lake’s water ecology using the Benthic Index of Biotic Integrity (B-IBI) provides a foundation for lake conservation and management. On the basis of benthic animal data collected from ten monitoring sites in Longgan Lake in April 2021, a comprehensive integrity index evaluation system was developed. The system comprises five core parameters: total species count, percentage of dominant group, percentage of mollusks, number of sensitive species, and number of adhesive species. Through analysis of the distribution range, discriminatory ability, and correlation of twenty candidate biological indicators, the most relevant parameters were identified. The dimensions of the biological parameters were standardized using the ratio method, and the scores for each parameter were aggregated to derive the B-IBI value. Lake health classification standards were established using the quartering process. The results revealed that among the ten monitoring sites in the lake area, three were classified as healthy, four as sub-healthy, two as fair, and one as poor. The overall water ecosystem health condition is not promising. The southeastern part of Longgan Lake was classified as healthy, while the water area at the border between Hubei and Anhui Provinces was categorized as sub-healthy, and the northeastern part as fair. The relatively poor health condition in the northeastern part of Longgan Lake may be attributed to its proximity to the entrance of the Erlang River, where the accumulation of domestic sewage and phosphate mining pollutants in the sediment has consequently impacted the integrity of benthic organisms.

Key words: macrozoobenthos, index of biological integrity, health assessment, Longgan Lake, Huayang river and lake group