The food of Chironomus crassicaudatus midge larvae in Lake Monroe, central Florida, was investigated from May 1981 to April 1982. Gut contents of larvae collected monthly from 16 stations in the lake were analyzed. Quantitative samples of water collected monthly at the mud-water interface at each station were analyzed for the larval food composition in the water. The larvae fed primarily on Cyanobacteria (blue-green algae). Blue-green algae were predominant in the water as well as in the larval guts, forming 63-87% and 52-84% of the total organisms observed in the water and in the larval guts, respectively. Populations of these organisms in the water were lowest in the summer. A highly significant relationship existed between the monthly mean percent of blue-green algae in the larvae and in the water. In general, the larvae were nonselective feeders in that the organisms enumerated in the water were also found in the gut.