This study looked at how to figure out where pollution in rivers comes from and how much there is. They focused on a place with a lot of pollution sources in its river network. The scientists examined different types of pollution sources and how they affect the water. They came up with a method to figure out how many pollutants each source lets into the river. They tested their method in Zhangjiagang City and found out how much pollution is going into the rivers there. This information can help the city plan and manage how to keep their water clean.