Co-authored by research scientists at the U.S. Environmental Protection Agency's Large Lakes Research Station, Grosse Ile, Michigan. This article discusses the resurrection, evaluation and application of a historical water quality model to provide estimates of the future trophic status in Lake Michigan. It is also shown how a relative simple mathematical modeling framework can be used as a diagnostic tool to guide scientists in developing the next generation of models for Lake Michigan and the other Laurentian Great Lakes.