Spatial variability of lake surface energy balance and its causes are not understood well. 90-m resolution energy balance maps of Lake Kasumigaura (172 km2) in Japan obtained by interpolating stations’ data and bulk equations allowed investigation of these issues. Due to lake-scale variation in meteorological variables and small-scale fluctuations of surface temperature Ts, surface heat fluxes were found differed horizontally at two distinctive scales while radiative fluxes were more uniform. The key variable Ts to surface fluxes was only homogenous for directions with a longer fetch or under calm wind conditions. Using these findings, the suitability of flux station locations, one at the center of the lake and another within a cove, were considered. Although both locations satisfied the fetch requirements, Ts was not always found to be homogeneous in the cove, making this location less suitable for flux measurements, an issue that has been overlooked in scientific communities.