The Ofunato Bay in Iwate Prefecture, Japan, is a deep coastal bay located at the center of the Sanriku Rias coast and considered an economically and environmentally important asset. Here we present the first whole genome sequencing (WGS) study on the microbial communities of the Bay where surface water samples were collected in 2015 from three stations along its length to cover the entire bay. We sequenced 0.2-??m filter fraction, targeting the free-living fraction only, among the sequentially size-fractionated samples of 20.0-, 5.0-, 0.8- and 0.2-??m filters,. As expected, Proteobacteria (Alpha, Beta and Gamma) were the most abundant phyla in the Ofunato Bay followed by Bacteroidetes, Firmicutes, Actinobacteria, Cyanobacteria and Tenericutes. We detected a wide range of heterotrophic bacteria, Archaea and eukaryotic algae. The majority of these bacteria are considered significant in oceans and marine ecology.