Abstract: A method and system for inactivating harmful organisms (e.g., red tide algae and dinoflagellates). The method includes the steps of supplying ambient air to a conditioning unit to generate conditioned air; passing the conditioned air to an ozone generator to generate ozone; mixing the ozone with water, from a water source, that contains the harmful organisms to generate ozonated water; delivering the ozonated water back to the water source to achieve dilution of the harmful organisms; at least partially isolating the water source from external water to prevent quick dilution of the ozonated water; and continually circulating water in the water source through the mixing step. The harmful organisms are inactivated by exposure to the ozone.