The researchers studied the levels of chlorophyll a in the Qiantang River in Hangzhou and how they relate to environmental factors. They found that chlorophyll a levels were higher in summer and autumn, and lower in winter and spring. Temperature had a positive correlation with chlorophyll a content. The transparency of the water and the levels of nitrogen and phosphorus also affected chlorophyll a levels. The river had enough nitrogen and phosphorus for algae growth, suggesting they are not limiting factors.