I examined responses of cisco (Coregonus artedi) to hypolimnetic oxygenation in Amisk Lake during the summers of 1989-1992. One basin of this double-basined eutrophic lake was oxygenated, whereas the second basin, and the nearby, untreated Baptiste Lake, served as reference systems. Dissolved oxygen (DO) concentrations in the hypolimnion of both basins of Amisk Lake increased during treatment but were higher in the treated basin than in the reference basin. Hypolimnetic DO in the treated basin remained above concentrations avoided by cisco ($<$1.3 mg$\cdot$L$\sp{-1})$ but fell below this level by mid-summer in the reference basin. Consequently, cisco habitat extended up to 8 m deeper in the hypolimnion of the treated basin than in the reference basin. Variations in monthly densities suggested that cisco in Amisk Lake also responded to hypolimnetic oxygenation by migrating from the reference basin into the treated basin. This behavioral response, coupled with deeper vertical extensions of fish habitat, resulted in the treated basin supporting a density and biomass of fish that was twice as great as in the reference basin. Higher DO concentrations enabled cisco in the treated basin to feed deeper into the hypolimnion, and incorporate more benthic species into their diets, than those in the reference basin. Increased DO concentrations in both basins resulted in expansion of whole-lake cisco habitat, and whole-lake fish density increased 5-fold and corresponding biomass tripled during treatment. Although prey base for cisco increased during oxysenation, per capita food quantity decreased. Growth rate and condition of cisco in Amisk Lake also decreased during treatment years cnmpared with pretreatment data, suggesting a density-dependent relationship with biomass. In contrast, in llntreated Baptiste Lake, where the hypolimnion remained anoxic each summer, cisco were restricted to epilimnetic waters, and density, biomass, and growth rate remained low. These results suggest thst through expansion of suitable habitat, hypolimnetic oxygenation can enhance cold-water fish production, especially if combined with regulated fish exploitation.