Much of the effort in assessing water quality changes is ineffectual because most of the water quality models and Geographic Information Systems (GIS) that are used in water quality management decision-making do not include the experience, judgement and expertise of water and wastewater quality specialists. The Water Quality Forecasting and Management Decision-Support Tool is a combination of engineering methods and recent advances in computer technologies of a rule-based object-oriented Expert System, GIS, and Dissolved Oxygen Sag simulation model. It is capable of analysing spatially distributed data, simulating river-quality response to varying organic waste loading and stream flow conditions; and interpreting its output results to minimise the demands on the ability of users.