Bathymetry for St. Catherines/Sapelo Sounds was derived from eighteen surveys containing 70,555 soundings. No surveys were omitted. The average separation between soundings was 52 meters. Fifteen of the eighteen surveys used dated from 1934. The remaining three surveys located in the east and south dated from 1974 and 1977. The total range of sounding data was 1.5 meters to -20.1 meters at mean low water. Mean high water values between 2.0 and 2.4 meters were assigned to the shoreline. Six points were found that were not consistent with the surrounding data. These were removed prior to tinning. DEM grid values outside the shoreline (on land) were assigned null values (-32676). St. Catherines/Sapelo Sounds have eleven 7.5 minute DEMs and a single one degree DEM. The 1 degree DEMs were generated from the higher resolution 7.5 minute DEMs which covered the estuary. A Digital Elevation Model (DEM) contains a series of elevations ordered from south to north with the order of the columns from west to east. The DEM is formatted as one ASCII header record (A- record), followed by a series of profile records (B- records) each of which include a short B-record header followed by a series of ASCII integer elevations (typically in units of 1 centimeter) per each profile. The last physical record of the DEM is an accuracy record (C-record). The 7.5-minute DEM (30- by 30-m data spacing) is cast on the Universal Transverse Mercator (UTM) projection. It provides coverage in 7.5- by 7.5-minute blocks. Each product provides the same coverage as a standard USGS 7.5-minute quadrangle but the DEM contains over edge data. Coverage is available for many estuaries of the contiguous United States but is not complete.