This document presents a comparison of predicted phosphorus and hypolimnetic oxygen concentrations with observations from Lake Simcoe for the period 1970-1990 using a mass balance model. It then uses the model (i) to predict the effects of phosphorus management strategies upon oxygen conditions to assist the Lake Simcoe Environmental Management Strategy in evaluating the consequence of controlling phosphorus loadings, and (ii) to provide a historical perspective for eutrophication over the period 1970-1990 and from 1800 to present. The technical findings of the three phases of this study are presented in this report and four others (BEAK, 1987, 1990, 1992a, and 1992b).