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ABSTRACTWe tested a previously published empirical multivariate regression model that predicts end-of-summer oxygen concentrations in the hypolimnia of small, dilute lakes in the Boreal ecozone. The model inputs include only lake morphometry and total phosphorus concentration at spring-overturn. In this study, we tested the validity of the model using information for lakes that are larger or deeper, and have higher phosphorus concentrations than the lakes that were the basis for the original regression model. Data from 32 lakes in the Gull River watershed in central Ontario and 10 lakes in eastern Ontario were used to evaluate the model's ability to predict end-of-summer oxygen profiles. Results indicated that the original model was satisfactory for most of the 42 study lakes, but had more limited success in the deeper and larger lakes within the data set. For the eastern Ontario lake set, the original model's ability to predict oxygen in the hypolimnia was better than for the Gull River watershed lakes. It is suggested that the most useful application of the model would be to predict the change in hypolimnetic oxygen concentrations at given depths that would result from increases or decreases in total phosphorus concentrations in the lake. This would allow resource managers concerned with sportfish habitat, to estimate and assess the impact that changes in lake trophic status might have on oxygen concentrations.