The water quality of the Poyanghu Lake during 1985-2013 was investigated and assessed. The results show that the water quality presented a decreasing trend, the current eutrophication status was moderate, and the main pollutants were the total phosphorus (TP) and ammonia nitrogen (NH3-N). By using the seasonal Kendall test for the main pollutants of TP and NH3-N, it was found that TP and NH3-N appeared a significantly rising trend for most of monitoring cross-sections into or in the lake and the controlling-sections in the lake outlet.