MINLAKE, a dynamic, one-dimensional, unsteady lake water stratification simulation model has been extended by a water jet mixing submodel (JETMIX). The model is intended primarily to evaluate lake management and control strategies. The extended model simulates the continuous change of lake stratification in response to artificial mixing induced by water jets and natural mixing by wind and cooling. Artificially forced summer destratification with a recirculating pump/jet discharge system, and a warm water jet discharged into an ice-covered lake were studied. Numerical results were obtained to predict the effect of jet mixing on the evolution of water temperature and dissolved oxygen profiles in time. The effect of the warm water jet discharge on the ice cover was of particular interest. The simulation model was verified with laboratory experimental data. The capabilities and applicability of the model were illustrated with simulations of a hypothetical summer destratification and a planned winter discharge. The results can be used to design a hydraulic jet-mixing system for a lake or reservoir in summer and a submerged thermal outfall for year-round conditions.