The water quality of Poyang Lake has been declining due to increased nutrient loads from inflow rivers. TN and TP were the main factors causing this decline. The "Five Rivers" experienced a significant decrease in water quality from 2004 to 2011, leading to overall lower water quality in the lake. The southern and eastern areas of the lake had higher TN concentrations, while the southern area had higher TP concentrations. Changes in nutrient loading had a greater impact on water quality than changes in hydrological conditions.