Water temperatures and dissolved oxygen (DO) concentrations in lakes are related to climate. Temperature and DO in 27 lake classes (3 depth classes x 3 surface area classes x 3 trophic states) were simulated by numerical models with daily weather data input. The weather data used are from the 25-yr period 1955-1979. The lakes and the weather are representative of the north- central U.S. Daily profiles of water temperature and DO concentrations were computed and several temperature and DO characteristics extracted from this information base. Temperature and minimum oxygen requirements for good growth of cold, cool, and warm water fish were then applied to determine the length of the good-growth periods and the relative lake volumes available for good growth. All characteristics are presented in graphical form using lake surface area, maximum lake depth, and Secchi depth as independent variables. The surface area and maximum depth were combined in a lake geometry ratio which is a relative measure of the susceptibility of a lake to stratification; Secchi depth was retained as a measure of lake transparency and trophic state. To determine an effect of latitude, we investigated a southern and northern region separately. The effect of climate change due to a projected doubling of atmospheric CO2 was investigated by applying the output from the GISS 2 x CO2 global circulation model to the lake models.