Par Pond and L Lake are cooling reservoirs located on the Savannah River Site in South Carolina. Large beds of aquatic macrophytes (primarily cattail and waterlilies) exist in Par Pond and are now beginning to develop in L Lake. Biophysical knowledge about Par Pond was used to develop «environmental constraint criteria» to predict the future spatial distribution of aquatic macrophytes in L Lake. The L Lake biophysical data were placed in a 5- by 5-m raster geographic information system (GIS) and analyzed using Boolean logic.