The surface energy balance (SEB) of a freshwater body must incorporate shortwave (solar) and long-wave (terrestrial) radiation, together with evaporation and sensible heat energy fluxes. For inclusion in a prognostic water quality model it is vital to be able to calculate, rather than measure, these energy terms and to relate them to routinely observed meteorological parameters such as air temperature and cloud cover. Here various formulae are analyzed and compared by using two climatologically different data bases. For shortwave radiation the formulae recommended for use, in the dearth of local observations, are those of Prescott (1940) (for temporal scales of weeks or months) and Tucker (1982) (for shorter time scales). The shortwave albedo can be given by the parametrization of Pivovarov (1972), the incoming long-wave atmospheric radiation by a blackbody representation modified by an effective atmospheric emissivity (Raphael, 1962), and the evaporative flux by the equation of Sill (1983), with the sensible heat flux being related to the evaporative energy flux via the Bowen ratio under conditions of neutral atmospheric stability.