A variety of viral particles, the majority of them clearly identifiable as bacteriophages, were found in the seawater of Yaquina Bay, Oregon. These phages were obtained as free particles from the seawater without employing specific hosts for enrichments or further purification in the laboratory. A variety of electron micrographs showing different morphologies of phages as well as phage-bacterium interactions found in the seawater are presented. In the area where the bay received organic enrichment from seafood processing plants, a minimum of 10(4) phage particles per ml was estimated. Since the technique used was designed to concentrate particles 0.2 micrometer in diameter or larger it is assumed that the actual number of phage particles is higher than 10(4) particles per ml. The implications of the presence of such phage concentrations in bays and estuaries with a certain level of eutrophication are of obvious importance in considering the microbial ecology of these environments.