Among common estuarine submerged plants, seagrasses are the most extensively studied due to their ecological importance in estuarine ecosystems. Seagrass meadows are important biological habitats for a wide variety of marine animals and plants. They are a source of organic carbon for commercially important animals. Furthermore, seagrasses act as nutrient filters in estuarine and coastal marine ecosystems. As such, mapping the distribution of seagrass beds is important for management and conservation strategies. In order to survey the seagrass distribution within the Seomjin Estuary, We directly observed seagrass beds in Kwangyang and Hadong using SCUBA. The distribution area, species composition, morphology, density, biomass and productivity of seagrass meadows were examined. Seagrass meadows were distributed in the intertidal and subtidal zones of the Galsa tidal flats, and in the subtidal zone of the neighboring POSCO area. Patches of Zostera japonica was found at patches at the Galsa tidal flats intermediate point. The total estimated seagrass distribution area of the Seomjin Estuary was $1.84;km^2$. Of the total, $1.83;km^2$ was Zostera marina (eelgrass) and $0.01;km^2$ was Zostera japonica (dwarf eelgrass). Zostera japonica was found in intertidal zones. Zostera marina was found from the intertidal to subtidal zones at a 2 m mean sea level (MSL) depth. The leaf productivity of Zostera marina was $4.47g;DW;m^{-2};day^{-1}$. The annual production of eelgrass was $1,632;g;DW;m^{-2};yr^{-1}$, which corresponds to $731g;C;m^{-2};yr^{-1}$. The total production of eelgrass was $3,002;tons;DW;yr^{-1}$, which corresponds to $1,343;tons;C;yr^{-1}$.