This study addressed the relationship of river water pollution characteristics to land covers and human activities in the catchments in a complete river system named Cao-E River in eastern China.Based on the hydrogeochemical data collected monthly over a period of 3 years,cluster analysis(CA)and principal component analysis(PCA)were adopted to categorize the river reaches and reveal their pollution characteristics.According to the differences of water quality in the river reaches and land use patterns and average population densities in their catchments,the whole river system could be categorized into three groups of river reaches,I.e,non-point sources pollution reaches(NPSPR),urban reaches(UR)and mixed sources pollution reaches(MSPR).In UR and MSPR,the water quality was mainly impacted by nutrient and organic pollution,while in NPSPR nutrient pollution was the main cause.The nitrate was the main nitrogen form in NPSPR and particulate phosphorus was the main phosphorus form in MSPR.There were no apparent trends for the variations of pollutant concentrations with increasing river flows in NPSPR and MSPR,while in UR the pollutant concentrations decreased with increasing river flows.Thus dry season was the critical period for water pollution control in UR.Therefore,catchment land covers and human activities had significant impact on river reach water pollution type,nutrient forms and water quality responses to hydrological conditions,which might be crucial for developing strategies to combat water pollution in watershed scale.