Abstract: To reasonably evaluate the eco-environmental health status of the Gan River,the periphytic algae community structure and water environmental characteristics at 11 sites in the Gan River in June 2023 were investigated and analyzed.The community structure characteristics of the Gan River's periphytic diatoms were studied using McNaughton dominance index and cluster analysis.The response mechanism between the structure of periphytic diatom communities and water environmental factors was investigated using principal component analysis,Spearman correlation analysis,and canonical correspondence analysis.The results showed that a total of 80 species (varieties) of periphytic diatoms were identified in the Gan River,indicating high species richness,although species richness varied greatly among sites.The overall water eco-environmental quality of the Gan River was relatively healthy,with the highest abundance of clean indicator species among the periphytic diatom communities.Among them,Achnanthidium minutissimum had a dominance of 0.37,making it the absolute dominant species.Based on cluster analysis of different sampling sites,the 11 sites were divided into three groups.From Group 1 to Group 3,the average values of species richness and Shannon diversity index first increased and then decreased,while the average value of the Pielou evenness index showed a significant increasing trend,and the cleanliness of the dominant species decreased.The main water environmental factors affecting the periphytic diatom community structure in the Gan River were QHEI,pH,NH₃-N,TDS,and COD,among which NH₃-N was the main influencing factor for Group 2,and COD was the main influencing factor for Group 3.As a result,periphytic diatom communities can effectively indicate the nutrient status of the Gan River.