Lap An lagoon located in the key economic area of Phu Loc district, is one of the places in the local planning of socio-economic development. In addition, Lap An lagoon is also an intermediate area for transporting water between the mountains and Lang Co bay. The change of Lap An lagoon water quality in Thua Thien Hue province was assessed through the analysis of water quality parameters from 2005 to 2008. The monitoring results indicate that the water quality was good with all parameters meeting the Vietnamese standards. However, water quality of influent streams is potentially polluted, especially by heavy metals, nutrients and coliform. This impacts on water quality of Lap An lagoon.