The study looked at how water flowing back from a reservoir affects the nutrient levels in the Xiangxi River in China. By analyzing data from 2014 to 2016, researchers found that the amount of nutrients in the river decreased when more water flowed back from the reservoir. This decrease was seen in various types of nutrients, like nitrogen and phosphorus. They also found that changing the flow of water between the reservoir and the river can help prevent harmful algae from growing in the river. By controlling this water flow, the water quality in the Xiangxi River can be improved.