The surplus production model, a conventional fishery stock assessment model, is applied to assess the entrainment and impingement impact of the Monroe Power Plant on the yellow perch standing stock and fishery in the western basin in Lake Erie. Biological parameters of the model are estimated from commercial catch and effort data and entrainment and impigement coefficients are estimated from power plant data. The model is applied to estimate stock biomass, egg production, and larva production; the proportions entrained and impinged are then estimated. The impact of water withdrawal on the equilibrium standing stock and maximum sustainabble yield from the fishery is estimated and the impact of increased water withdrawal is simulated.