The researchers studied the problem of too much plant food (eutrophication) in a lake in Tianjin. They looked at the amount of chlorophyll-a, a sign of too many nutrients, in the water from March to September 2013. They found that chlorophyll-a levels were highest from June to September and were influenced by factors like water temperature and phosphorus. Phosphorus was the most important factor in controlling the lake's health. To keep the lake healthy, it's important to reduce phosphorus levels, especially from June to September.