The researchers studied the water quality of Lake Poyang in China from 2009 to 2014. They used a method called the Water Quality Index (WQI) to assess the water quality. The results showed that the overall water quality was "moderate", but it was getting worse over time. Water quality was best in summer and worst in winter. Nutrient levels, like total nitrogen and total phosphorus, had the biggest impact on water quality. Toxic metals and other parameters were generally at safe levels. Water level had a positive effect on water quality by diluting pollutants. It's important to monitor and manage nutrient levels, especially during low-water periods when water quality is worse.