The researchers studied water quality in Lake Dongting, China from 1983 to 2004. They used a method called Nemerow Index to analyze how water quality changed over time and space. The results showed that water quality in the lake fluctuated, with serious pollution in 1988 and improvements in later years. Total phosphorus was the main pollutant. Water quality was worse during flood season but improved after 2002. Pollution was more severe in the riverways entering the lake than in the lake itself, with the worst water quality in Lake West Dongting.