A retrospective analysis was conducted of the response of Saginaw Bay, Lake Huron, to a substantial reduction in external phosphorus loadings over the study period 1974-1980. Loadings to Saginaw Bay from the Saginaw River for total phosphorus and dissolved ortho phosphorus were 55% and 72% lower, respectively, in 1980 than in 1974. In the most seriously degraded area of the bay, spring and fall total phosphorus concentrations decreased by 1% and 14%, respectively, while chlorophyll a concentrations decreased by 53% and 61% in the same seasons. The corresponding decreases for inverse Secchi depth were 0% and 17%. Sediment resuspension due to wind-induced wave action was the probable cause for the anomalous relationship between chlorophyll a and total phosphorus concentrations, and the lack of response of inverse Secchi depth. A substantial decrease in threshold odor observed in the municipal water supply during the study period was correlated with a decrease in blue-green dry weight biomass concentration.