The applicability of chlorine to control Ocean Thermal Energy Conversion (OTEC) biofouling was investigated. Onsite hypochlorite generation was found to be the preferred method of chlorination. The major fouling organisms of concern to OTEC are the microfouling organisms, that is, initial slime layers. However, macrofouling organisms may become a problem after several years of plant operation. Continuous low-level chlorination is more effective against hard-shelled macrofouling organisms and soft-shelled organisms, whereas intermittent chlorination will control slimes and soft-shelled organisms. Actual on-site experimentation is needed before effective doses and chlorination regimes can be recommended. The doses and regimes may vary depending upon whether the condenser and/or evaporator heat exchangers are chlorinated.