The Eastern oyster (Crassostrea virginica) is an economically important fisheries resource along the US Gulf Coast and the eastern seaboard. In the past few years, Mississippi has ranked second in the country in shellfish production, harvesting an average of 350,000 sacks (~15.8 million kg of oysters) per year. A GIS-based decision support tool was developed to aid the Mississippi Department of Marine Resources in managing shellfish in the state. The tool was designed using the ESRI ArcGis 8.3 Arcview software, which enabled us to integrate GIS data layers (e.g., oyster reef sites) with a program that automatically obtains Pearl River stage (gage height) and rainfall amount data from the USGS and NOAA websites, respectively. The program then compares the data with established area-specific standards and makes recommendations to the shellfish manager on the area(s) that should be closed or opened. The decision support tool is the first tool developed for shellfish management in the US Gulf Coast area. Although it was developed for use in Mississippi, it can be modified for use in other states. It simplifies the shellfish management process and maintains a database of the water quality data and the management actions that have been taken, thereby facilitating data analyses and preparation of reports.