The structure of bluegill (Lepomis macrochirus) populations in natural Florida lakes was assessed from electromorphic and morphologic characters. Electrophoretically assayed allele frequencies are homogeneous within lakes and heterogeneous among lakes. Populations in two adjacent lakes connected by a short river are nearly identical. Several considerations indicate that even young-of-the-year bluegills are well mixed within subpopulations of these lakes, and that individual dispersal is important in maintaining intersubpopulation homogencity in allele frequency. This pattern of genetic differentiation contrasts with the pattern of heterogeneity observed in meristic counts for several morphological traits. At the microgeographic level, genetic homogeneity probably reflects a long-term history of bluegill movements within a lake, while within-lake morphological heterogeneity reflects the varied conditions during individual development to which incompletely isolated subpopulations are exposed.