To cope with the growing challenge of water pollution by nutrient-rich wastes, excessive growth of phytoplankton may be controlled by diverting wastes into other receiving waters or by treating the wastes to remove growth-promoting substances. Phosphorus recovery appears to be an effective and practical means of controlling aquatic growths, but an economically feasible process awaits development. In an experimental inquiry into the usefulness of algae for recovering phosphorus from sewage, a high-rate process was developed in the laboratory whereby soluble phosphorus reductions equivalent to 90 percent or more were achieved with contact times as brief as 6 to 12 hours. Subsequent studies in the field on a larger scale showed the effectiveness of the process to be related to available light intensity. Photosynthetic adjustment of pH permitted rapid removal of phosphorus through coagulation and sedimentation. Repeated use of algal cell tissue in conjunction with high photosynthetic pH levels greatly enhanced the recovery of algae by sedimentation.