A deterministic, spatially segmented, multi-class phytoplankton model is calibrated to an extensive set of field data acquired on Saginaw Bay, Lake Huron, during 1974 and 1975. Significant differences between observed mean values from the field data, and mean values computed by the model output and field data for 86% of the sampling cruises in the principal spatial segments. Seasonal mean values between model output and field data are also compared because of hydrological and productivity cycles. Discrepancies occur for water column total phosphorus concentrations. The resuspension mechanism in the calibrate model accounts for 36 and 68%, respectively, of the computed spring and fall average total phosphorus concentrations.