Abstract: A method of preventing fouling organisms in marine environments comprises the step of introducing into the marine environment in a predetermined form and in a sufficient amount an antifouling composition having as its effective ingredient a nitric oxide-releasing functional group of the diazeniumdiolate structure: whereupon nitric oxide is controllably released into the marine environment to prevent at least one of the fouling organisms' propagation, ability to attach, and ability to function. An antifouling composition consists essentially of an antifouling-acceptable carrier and a coprecipitation product of polylactide/glycolide and diethylenetriamine having the formula H3N+CH2CH2N(N2O2)−1CH2CH2NH2, wherein diethylenetriamine contains a nitric oxide-releasing functional group.