An investigation in Northern China studied how releasing water from upstream reservoirs affects river water quality before it reaches Baiyangdian Lake. They looked at two routes: WangKuai and XiDaYang reservoirs. Overall, pollutant levels increased downstream along the WangKuai route, with water quality near the lake falling short of targets. Along the XiDaYang route, pollution peaked after Baoding city but improved further downstream, with only total nitrogen levels surpassing standards. The different distribution of wastewater treatment plants in these routes caused variations in pollution patterns.