Improved water pollution index for determining spatiotemporal water quality dynamics: Case study in the Erdao Songhua River Basin, China

•A holistic water quality assessment was conducted in the Erdao Songhua River Basin.•The IWPI showed “Good” water quality with spatiotemporal variations in studied basin.•PI, DO, CODcr, and BOD5 are the most important parameters in this basin.•The potential risks of point source and non-point source pollution in middle-downstream should be of concern. The Erdao Songhua River provides drinking water for 16.82 million people; therefore, ensuring that the water quality adequate is of particular concern. In this study, an improved water pollution index (IWPI) and multiple statistical methods were employed to assess the overall water pollution situation and investigate spatiotemporal variations of seven physicochemical parameters such as the permanganate index (PI), dissolved oxygen (DO), chemical oxygen demand (CODcr), five-day biochemical oxygen demand (BOD5), total nitrogen (TN), total phosphorus (TP) and ammonia nitrogen (NH3-N), which were collected monthly at 20 sites within the mainstream and major tributaries of the Erdao Songhua River Basin (ESRB) from 2015 to 2020. Stepwise regression analysis was conducted to build a minimum improved water pollution index (IWPImin) model consisted of four key elements (PI, DO, CODcr, and BOD5) proposed from seven parameters. The results demonstrated water quality within the ESRB was considered to be “Good” with the mean IWPI values