The researchers studied the water quality of Lake Changhu in Hubei Province to understand its eutrophication status. They monitored 20 sites over two years and found that the lake was eutrophic, meaning it had excessive nutrients causing algae growth. The main factors contributing to eutrophication were phosphorus and nitrogen pollution, with nitrogen being more influential in summer and autumn. The researchers suggest implementing measures like reducing external phosphorus input and promoting aquatic plants to improve water quality and prevent severe eutrophication in the future.