Eelgrass (Zostera marina) is an essential habitat for the Great Bay Estuary (GBE) because it provides food for wintering waterfowl and habitat for juvenile fish. Eelgrass is the basis of an estuarine food chain that supports many of the recreationally, commercially and ecologically important species in the estuary. Additionally, eelgrass filters estuarine waters, removing both nutrients and suspended sediments from the water column. Eelgrass in the Great Bay Estuary is the largest monoculture in the State of New Hampshire and is considered a vital resource to the States marine environment. The UNH Seagrass Ecology Group has mapped the distribution of eelgrass in Great Bay every year from 1986 to 2001 (Short, unpublished data). Eelgrass in the entire Great Bay Estuary system (Great Bay, Little Bay, tidal tributaries, Piscataqua River, and Portsmouth Harbor) was mapped in 1996, and from 1999 through 2003. Eelgrass cover in Great Bay has been relatively constant for the past 10 years at approximately 2,000 acres. Earlier, in 1989, there was a dramatic decline in eelgrass beds to only 300 acres (15% of normal levels). The cause of this crash was an outbreak of a slime mold, Labryrinthula zosterae, commonly called wasting disease. Recently, the greatest extent of eelgrass in the GBE was observed in 1996. The University of New Hampshire provided digitized eelgrass distribution information in Great Bay Estuary for the years 1999-2001 to NHEP database. Additionally, the 2002 eelgrass coverages are now in the NHEP database. In 2004, the NHEP funded annual monitoring for eelgrass in GBE. We collected aerial photography of eelgrass coverage for 2004 and mapped eelgrass distribution for 2003 from the information gathered the previous year. The present report presents the eelgrass distribution information for 2003.