The study looked at water quality in the catchment area of Miyun Reservoir, a vital water source for Beijing, China. Eutrophication, or excess nutrients in the water, was a big issue there. Researchers found that total nitrogen pollution was at its worst level. They sampled water at 52 sites over a few months and saw that Bai River had better water quality compared to Chao River. Tributaries generally had cleaner water than the main rivers. The middle parts of rivers in Hebei Province had the most pollution. The cleanliness of the water was linked to how the land in different areas was used. The study suggests that improving water quality could benefit from a fair payment system, especially in Hebei Province.