This manuscript describes the verification of a calibrated mathematical model designed to predict the spatial and temporal distribution of Cladophora about a point source of nutrients. The study site was located at Harbor Beach, Michigan, on Lake Huron. The model is intended to have a widespread utility for evaluating the impact of phosphorus removal on the nuisance growth of Cladophora. Therefore, verification was attempted by implementing phosphorus removal at the study site. Phosphorus removal efficiencies at the Harbor Beach, Michigan, wastewater treatment plant averaged 80-90% following the implementation of alum precipitation. The average loading of soluble reactive phosphorus was reduced from 1.35 kg P/day in 1979 to 0.20 kg P/day in 1980. The standing crop, areal distribution, and duration of abundance of Cladophora biomass were considerably reduced in 1980. (Copyright (c) Internat. Assoc. Great Lakes Res., 1982.)