This work was aimed at investigating the feasibility of using mixed microbial culture (MMC) for improving the river water quality. Upon the release of the MMC into the river water at various ratios (v/v), 1:2500 was found to be the best ratio to reduce the nutrient concentration in river water. At this ratio, although the concentration of microorganisms increased significantly, the Cyanobacteria levels decreased during the four seasons, i.e. 31.4, 16.5, 60.5 and 55.7%, respectively, during the spring, summer, autumn and winter seasons. The chemical oxygen demand (COD), ammonia nitrogen (NH3-N), nitrate nitrogen (NO3-N), total nitrogen (TN) and total phosphorus (TP) removals by MMC were 76.5, 73.8, 71.7, 75.8 and 67.2%, respectively, during the autumn season. Finally, the study was extended to a demonstration project in Yudai river, Zhengjiang, Jiangsu, China to demonstrate the effect of MMC addition on river water quality improvement. At the end of the 8 weeks experiments, the average COD, NH3–N, NO3–N, TN and TP removal efficiencies were 46.4, 51.3, 43.9, 41.7 and 46.4%, respectively. © 2020 Elsevier B.V.