TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Method: The step of culturing the organisms involves replenishing the eutrophic water in the enclosure with algae, and does not involve adding fish meal, fish oil, nitrogenous fertilizer, and/or phosphorus fertilizer into the eutrophic water. The step of culturing the organisms involves maintaining the level of dissolved oxygen in the eutrophic water in the enclosure above 3 mg/l. The step of culturing the organisms involves mixing eutrophic water from outside the enclosure with the eutrophic water in the enclosure. The step of culturing the organisms involves moving the enclosure in the body of eutrophic water. The method further involves harvesting at least one of the organisms after culturing. The steps of introducing, culturing, and harvesting the organisms are repeated at least once or until the algal biomass is reduced. Preferred Components: The body of eutrophic water comprises more than of 1x 105 algal cells/ml, and the algal cells are cells of cyanobacteria, diatoms, dinoflagellates, raphidophytes, and/or haptophytes. The body of eutrophic water comprises an algal bloom, a harmful algal bloom, or a hypoxic zone; or where the body of eutrophic water is found in a location where an algal bloom, a harmful algal bloom, or a hypoxic zone has occurred previously. The dimension of at least one dominant species of algae is 200-2000 (preferably 20-200, especially 0.2-2) mu m. The dominant species in the eutrophic water is a species of Anabaena, Aphanizomenon, Microcystis, Noctiluca, Alexandrium, Prorocentrum, Gymnodinium, Ceratium, Pfiesteria, Dinophysis, Gyrodinium, Heterosigma, Chattonella, Skeletonema, Synedropsis, Pseudonitzschia, Leptocylindrus, Chaetoceros; Phaeocystis, Nannochloris, Stichococcus, Aureococcus, Miraltia, Guinardia, Spermatozopsis, Urosolenia, Nitschia, Cyclotella, Cryptomonas, or Pedinophora. The organisms that feed on algae comprise a population of fishes, a population of shellfishes, or populations of fishes and shellfishes. The organisms comprise planktivores and/or omnivores. At least one of the major species of planktivores is a pelagic phytoplanktivore. At least one major species of the organisms that feed on algae is a species of fish in the order Clupiformes, Siluriformes, or Cypriniformes. The organisms comprise at least one of any one of menhaden, anchovies, shads, sardines, pilchards, herring, smelts, catfish, milkfish, carps, mullets, and hilsa. The organisms comprise at least one of oysters, mussels, scallops, or clams. The enclosure is a floating cage, a submersible cage, a submerged cage, or a towable cage. The organisms comprise Brevoortia patronus or Brevoortia iyrannus which are confined to a floating cage. The organisms are fishes introduced at a density of 300-600, or 600-900 individuals/m2. The enclosure is a floating cage, a submersible cage, a submerged cage, or a towable cage. The enclosure is tethered to a vessel, inside a vessel, or tethered to an oil/gas production platform. Preferred System: The system further comprises an environmental monitoring system, a data system, a guidance system, or a fish processing facility. ACTIVITY - Antialgal. No biological data is given.    MECHANISM OF ACTION - None given.    EXAMPLE - No suitable example is given.