Wind velocity, air temperature, and humidity fluctuations were measured over Orange Lake, Florida, using an ultrasonic anemometer-thermometer and Lyman alpha humidity sensor. Latent and sensible heat fluxes were calculated from the data using the eddy correlation technique. Lake temperature at a 2.5-cm depth was measured in order to compare eddy correlation results with fluxes and the Bowen ratio predicted by the formulae of Hicks (1975) and Priestley and Taylor (1972) in which temperature is the sole parameter. Bowen ratio results were in good agreement with the formulations of Hicks (1975) and Priestley and Taylor (1972) if property values were evaluated at a temperature intermediated to the lake and 10-m air temperature. Disagreement with fluxes predicted by Hicks (1975) indicates that such formulations are inadequate for short-term flux evaluations under the meteorological conditions in which surface water temperature is changing with time.