Long-term trends (e.g. 1997~2010)of chlorophyll a and water quality properties of the Yeongsan River were analyzed by using water quality monitoring data collected by the water information system, ministry of environment. Nine monitoring stations were selected along the main channel of the river, and parameters of BOD, COD, TN, TP, conductivity, TSS and chlorophyll a were collected for surface water monthly through the monitoring system. Trends of water quality and chlorophyll a were analyzed by the Seasonal Mann=Kendall Test and LOWESS(Locally Weighted Scatter-plot Smoother).The results showed that the water quality parameters, including chlorophyll a, were improved in all stations except Station WC in the most0upper region, where water quality data for the determined parameters were increased, indicating a reduction in water quality. Based on the results from LOWESS analysis, chlorophyll a (algal blooms),BOD and COD recently began to increase after 2007 suggesting that an additional study on the cause of these increases in organic pollution, as well as a better management system for the region are required.