Emphasis on evaluation techniques where measured versus predicted changes of mass are compared can produce a model that predicts the correct answers for the wrong reasons. The movement of mass between compartments (flux) should be compared to measured flux as part of the model verification. Model verification techniques need to reflect the same level of resolution inherent in the model structure. The U.S. Corps of Engineers water quality model, CE-QUAL-R1, was verified for DeGray Lake, Ark., using this procedure. Several processes important in determining the mass of the constituents were measured for DeGray Lake. Primary production rate and settling rates of algae, total dry weight, and organic matter were compared to predicted fluxes. Results indicated that the model was satisfactory in predicting trends in flux values.