Abstract: In order to achieve the long-term improvement of the water environment of rivers in Tianjin central urban area, taking Balitai and Jizhuangziqiao as two typical river sections in Weijin River basin in the water transfer cycling route, the concentrations of NH₃-N, COD_Mn and COD_Cr were analysed. The results showed that pollutant concentration in non-flood season was low, but those in flood season significantly exceeded level V of surface water standard. The drainage of pumping station in flood season is an important reason for the increase of pollutant concentration in river. Hierarchical clustering method was used to identify the main pollution source. The results showed that the main pollution source in Balitai section was Shuangfengdao pumping station, followed by Haiguangsi pumping station. The pollutants in the Jizhuangziqiao section mainly came from the Meijiang pumping station, Tiyuan Bei pumping station and Wushui Road pumping station. Therefore, it is necessary to continuously monitor the drainage quality of the main polluting pumping stations during the flood season and adjust pump station discharge. The rainwater and sewage in the water receiving areas of the above main pollution pumping stations has not been fully separated, and some domestic sewage was overflowd into the river, so rainwater and sewage diversion in the pumping station is a long-term mechanism for improving the water quality of Weijin River.

Key words: central city, typical river, water quality change, pollution cause, system clustering