The researchers used a method called the trophic status index to check the health of Qionghai Lake. They looked at data from four different spots from 2008 to 2010. They found that the water near Haihe River is a bit too rich in nutrients, which is causing some issues. This is mainly because there is too much total nitrogen and phosphorous in the water, and it's getting less clear. They suggested some ways to stop this from happening.