Geographic information system (GIS) analysis with bathymetric, substrate, and side scan sonar (SSS) data was used to assess both spatial and temporal expansion of exotic dreissenid mussels onto sedimentary habitats in Lake Erie. These data were used for developing multiple regression models with substrate types and SSS data to interpret the expansion of Dreissena assemblages across the central and western basins of Lake Erie from 1994 to 1998. The 1994-1996 GIS model predicted the 1997 SSS measurements of Dreissena coverage correctly in 84% of the cases (n = 50). Similarly, the 1994-1997 GIS model predicted the 1998 SSS measurements of Dreissena coverage correctly in 80% of the cases (n = 20). These models indicated that Dreissena coverage ranged from$<$1% on muds in 1994 to 67% on sands and gravels in 1997. Based on all of the substrates, the 1994-1997 model indicates that Dreissena beds have been expanding since 1994 at 1,000 ± 6 km2yr-1and presently occupy 5,484 ± 32 km2of the 25,734 km2sedimentary bottom of Lake Erie. Our observations indicate that expanding Dreissena beds are altering soft-substrate habitats and influencing the ecosystem dynamics throughout Lake Erie. Furthermore, this study demonstrates that the distribution, abundance, and ecosystem impacts of invasive species in other watersheds can be accurately described and interpreted over diverse spatial and temporal scales using GIS models.