Abstract.-Characteristics of bluegill Lepomis macrochirus populations and fish communities were studied intensively at Dead Lake and Blueberry Pond. The lakes were small, shallow, and weedy, with macrophytes covering 41-83% of the surface. Both contained unusually high proportions and densities of bluegills over 8 in long due to unusually low fishing mortality, a favorable growth pattern, and low recruitment to age 2 or 3. Growth was rapid from 3 to 8 in, it then slowed and condition deteriorated among older fish. Mortality of adults was observed in early spring, when about 10% of the adults died. Rapid growth was stimulated by consistently low recruitment and utilization of limnetic Daphnia and littoral benthos as food. Low recruitment was partially due to predation; a diet study at Blueberry Pond estimated 303,300 juvenile bluegills per year were consumed by fish predators. Most juveniles were eaten by largemouth bass Micropterus salmoides, very few by cannibal bluegills. Each lake contained dense, slow-growing piscivores, but surprisingly they comprised less than 20% of the total fish biomass. It appeared that few adult bluegills attempted to spawn in Blueberry Pond, and this lack of spawning was likely more important than predation in controlling bluegill abundance. A supplemental pond study demonstrated that young and old adults of varying condition had normal reproductive potential. The triggering of spawning behavior may be linked to adult density, and perhaps adult growth, by behavioral or bioenergetic mechanisms. The implication for fisheries management is that weedy lakes need not be dominated by small, stunted bluegills but are capable of producing large bluegills if fishing harvest is restricted and a favorable food chain is present.