The shapes and sizes of the major oyster (Crassostrea virginica) reefs (beds) in New Hampshire have been determined using a variety of techniques. Langan (1997) used a combination of tonging and diver observations, coupled with buoys located by differential GPS, to map the boundaries of most of the major reefs shown in Figure 1. In 2001, four of these reefs (Nannie Island, Woodman Point, Adams Point, and Oyster River) were again mapped using different combinations of acoustic sounders, videography, and quadrat sampling. The present project required mapping the boundaries in order to determine the size of the remaining two major reefs in the Great Bay Estuary: Squamscott River and Piscataqua River. Underwater videography was used in the present study to determine the boundaries of these two reefs. The overall purpose of the present project was to complete the more recent (2001) mapping effort so that New Hampshire Estuaries Project (NHEP) will have information on areal coverage of the six oyster reefs regularly monitored by New Hampshire Fish and Game Department. The objectives of this project were to map the two study reefs, determine their areal coverages, and compare the new data with data from previous studies. Four deliverables were required: (1) Two ArcView-compatible GIS-based maps of the Squamscott River and Piscataqua River oyster reefs, (2) two photomontages constructed from 50+ stills extracted from video imagary of each reef, (3) documentation/metadata for the GIS file, and (4) copies of all video imagery.