This paper is about the development of a decision-support system for water-pollution management and environmental planning. More specifically, the paper first presents the overall concept and the system architecture of a generic environmental decision-support system (EDSS) and then develops an EDSS especially for analysing the tidal flow pattern and water quality of China's Pearl River Delta. The EDSS developed here employs the object-oriented approach to design the environmental database and utilizes the system integration technology to develop the overall user-friendly system that operates in the Windows environment. Furthermore, the system can be expanded to facilitate automated model selection and analysis. The EDSS should be of value for managing water quality of river networks with complicated flow patterns, such as that found in the Pearl River Delta.