Data files contain simulated mean, daily, offshore, water temperatures for 20 vertical depths (ranging 4 to 159 m below the surface) for 9 years in the 2040s (2041-2049) and nine years in the 2090s (2091-2099) at two sites in Lake Michigan. One site is located in the northern basin where the National Oceanic Atmospheric Administration (NOAA) has been maintaining a weather buoy since 1979 (buoy 45002: 45.344, -86.411). The other site is located in the southern basin where NOAA has been maintaining a weather buoy since 1981 (buoy 45007: 42.674, -87.026). Simulated water temperatures were generated by integrating atmospheric and hydrodynamic models.