Temperature was measured in the water, bottom sediments, and bog surrounding Stewart’s Dark Lake and Tub Lake, Wisconsin, five times during 1965–1966. A thermal probe was used to penetrate to depths to 8 m into the bottom.In the deepest water of Stewart’s Dark Lake, with no seasonal temperature fluctuation, a steady‐state thermal gradient (0.20°C/m) was observed in the bottom sediments. Thermal conductivity of these gelatinous sediments was measured at 1.10 × 10−3 cal cm/cm2 sec°C; thus prescribing a steady‐state heat flow of 2.1 × 10−6 cal/cm2 sec or 66 cal/cm2 year.The pattern of isotherms within the bottom sediments and bog demonstrates the importance of solar radiation and the effects of absorption and circulation within these lakes. Seasonal changes in isotherm patterns are similar for both lakes. Seasonal temperature fluctuations are largely damped at depths below 4 m in the surrounding bogs. There is a negative (into the sediments) steady‐state thermal gradient associated with the shoreline, but the gradient becomes positive lakeward and landward. Thus, with respect to mean sediment temperatures, each lake is surrounded by a relatively warm rim.The annual heat budget of the sediments at the shoreline in Tub Lake was 3,670 cal/cm2; at a water depth of 8 m, it was 70 cal/cm2. The mean annual budget for the entire sediments of Stewart’s Dark Lake was 730 cal/cm2 and for Tub Lake was 970 cal/cm2. These values represent about 10 and 12%, respectively, of the total annual heat budgets for the water in each lake. The heat budget of the sediments is dependent on the amplitude of temperature variations of the overlying water and the thermal properties of the sediment.