The scientists examined pollution in the Hanjiang River Basin, discovering that the water quality is worse in smaller rivers feeding into the main stream. Pollution levels rise from the river’s source to where it flows into another river. The main contaminants are COD, TP, and NH3-N, indicating organic pollution. They found that pollution mostly comes from agricultural runoff, city wastewater, and livestock waste, with diffuse pollution being more prevalent than specific discharge points.