Aquatic treatment systems can be designed to produce effluents meeting secondary and typical advance treatment effluent requirements on BOD, SS, and nitrogen compounds. In many situations, particularly those where the climate is mild or effluent requirements are seasonal, aquatic systems will be more cost effective than conventional treatment processes to achieve these wastewater treatment objectives. The feasibility of using aquatic systems to remove other contaminants common in domestic wastewaters has not been determined conclusively. It appears that their use in these applications will be limited. Site-specific factors will affect the performance of an aquatic system. The nature and probability of occurrence of these effects can not be predicted adequately from the data and design criteria reported to date. Consequently, pilot-scale studies to develop site-specific aquatic system design criteria and to verify system performance should be conducted prior to construction of a full-scale aquatic treatment system.