Multibeam bathymetric and sidescan-sonar data were collected during NOAA survey H11445 in Long Island Sound offshore of Plum Island, New York. Together with sediment and photographic data collected on USGS cruise 09059 on the R/V Rafael, these data were used to delineate areas of boulders and sand waves in the study area and characterize sea-floor environments. The near-shore sea floor contains boulders and gravel as indicated by high backscatter in the sidescan-sonar imagery. Farther offshore, the sea floor is smooth and gradually deepens. An isolated depression caused by tidal scour in the northwest increases beyond 100 m water depths and Plum Gut, a channel between Plum Island and Orient Point, has a bottom depth of 60 m. Sand waves are present around the northwest basin and on a shoal north of Plum Island where wave asymmetry suggests net sediment transport in a counter-clockwise direction around the shoal. Sand makes up the finest grained sediment in the study area and is represented in the sidescan-sonar imagery as low backscatter. The absence of mud reflects the strong tidal regime. Photography from 13 stations in the study area are used to characterize the sea-floor environment and note floral and faunal populations.