Numerous indices developed during the last 10 years to quantify the concept of trophic state turned out to be too ambiguous to be useful to lake managers. Based on empirical relationships between various water quality indicators, the most widely used indices use Secchi disk transparency, chlorophyllaconcentration, and total phosphorus as a measure of lake trophic state. Indices based on data from north temperate lakes, however, are not directly applicable to Florida lakes. Many Florida lakes are known to be nitrogen rather than phosphorus limited. Florida lakes also commonly have macrophyte problems which are not accounted for by such indices. A series of indices based on Secchi disk transparency, chlorophyllaconcentration, macrophyte abundance, total phosphorus concentration, and total nitrogen concentration were developed for Florida lakes. The Secchi disk index serves as a physical measure of trophic state. The public perceives water clarity as an important attribute of lakes, and Secchi disk transparency is a good measure of water clarity. The biological measures of trophic state are based on chlorophyllaconcentration and macrophyte coverage. Chlorophyllaconcentration is a good indicator of algal populations and macrophyte coverage is related to potential aquatic weed problems. Since phytoplankton and macrophytes compete for similar habitats, Florida's shallow lakes usually do not experience nuisance conditions of both these autotrophs simultaneously. The chemical measures of the trophic state are total phosphorus and total nitrogen concentrations. These elements are the principal nutrients limiting primary productivity in aquatic systems and therefore provide useful information on the nutritional status of lakes. When the lake is primarily phosphorus limited, based on the ratio of total nitrogen to total phosphorus concentration, the phosphorus trophic index is used. If the lake is nitrogen limited, based on the concentration ratio, the nitrogen index is used. Many Florida lakes are not limited by a single nutrient and are relatively well balanced. In this case an average of the nitrogen and phosphorus indices is used to determine the trophic status. The overall trophic state index for a Florida lake is determined by combining the appropriate values obtained from the physical, chemical, and biological indices. Over 570 lakes in the State were ranked by this method. The relative simplicity of the trophic index, combined with its accuracy and reliability, emphasizes its utility in statewide lake management.