This report summarizes the activities of the NH Department of Environmental Services (NHDES) Shellfish Program for the period of January 2003 to December 2003. The NHDES Shellfish Program conducts a number of activities to minimize the health risks associated with consuming shellfish, and to continue to comply with National Shellfish Sanitation Program guidelines. Among basic program functions is a routine water quality monitoring program, which involved the collection of nearly 800 samples at over 70 sites in 2003. The results of which are used to ensure that assessments of water quality for all areas are kept up-to-date. Weekly red tide monitoring was key to early detection of dangerous levels of Paralytic Shellfish Poisoning toxin in offshore waters in June, leading a nearly one-month closure to all harvesting in the Atlantic coastal waters. The programs pollution source identification and evaluation program involved the collection of nearly 400 water samples under a variety of environmental conditions. These data will be used to complete and/or update sanitary surveys for a number of shellfish growing areas. A number of other studies and sampling programs, including a November 2003 dye/dilution study of the Newmarket wastewater treatment facility, were also pursued. A particularly useful sampling program has been the initiation of postrainfall water and shellfish tissue sampling in conditionally approved areas. This program improved management decisions and increased harvesting opportunities in Hampton/Seabrook Harbor, providing data that drove decisions to open the flats on 11 of the 14 days that the harbor was available for harvesting.