A Web-GIS based coastal information network system is developed and applied to Saemangeum coast in Korea. The Saemangeum coast located in the mid-west of Korean Peninsula is now undergoing coastal development such as constructing 33 km long sea dyke with two sluice gates and yielding 40,100 ha of artificial lakes and reclamation land. The artificial lakes are accepting the terrigenous effluents as well as exchanging with the coastal waters through the sluice gates. Due to the coastal development project running longer than 10 years, environmental management focusing on the water quality control and protection of environmental vulnerability is the major concern of stakeholders.