The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA) and the Connecticut Department of Energy and Environmental Protection (CT DEEP), has produced detailed geologic maps of the coastal sea floor. Bathymetry, originally collected by NOAA for charting purposes, provides a fundamental framework for research and management activities in Long Island Sound, shows the terrain of the seabed, and provides information on sediment transport and benthic habitat. During April 2009 NOAA completed hydrographic survey H12012 offshore in the northeastern Sound, and during April 2010 and May 2010 bottom photographs and surficial sediment data were acquired as part of two ground-truth reconnaissance surveys of this area. Two interpretive data layers were derived from the multibeam echo-sounder and the ground-truth data used to verify them. For more information on the ground-truth surveys see: https://cmgds.marine.usgs.gov/fan_info.php?fan=2010-010-FA and https://cmgds.marine.usgs.gov/fan_info.php?fan=2010-015-FA.