A one-dimensional model of lake temperature, evaporation, and ice has been coupled in an interactive mode with the climate version of the National Center for Atmospheric Research/Pennsylvania State University regional (mesoscale) atmospheric model (MM4). The coupled MM4-lake model makes possible high-resolution simulations of climate in the proximity of large water bodies. Atmospheric variables required as input for the lake model are supplied by MM4 and simulated values of lake temperature, evaporation, and ice cover are supplied to MM4 by the lake model. We have tested the coupled model system with a 60-day, summertime simulation at Pyramid Lake, Nevada, and with a 10-day, wintertime simulation of the North American Great Lakes and vicinity. Both simulations were conducted at a 60-km resolution. Results from these tests indicate the coupled model system produces realistic simulations of lake temperature, evaporation, and ice cover and that the coupled system is applicable to simulations of regional climate change.