An investigation of the food chains leading to the production of Florida spotted gar, Lepisosteus platyrhincus DeKay, was conducted in a 3-mile section of the Tamiami Canal approximately 20 miles west of Miami. In this area these fish are extremely abundant, and those collected ranged in length from 10.5 to 24.4 inches. Collections of gar, forage fish, plankton, periphyton, bottom fauna, and physicochemical data were obtained at frequent intervals from February 20 to June 28, 1952. A total of 448 gar stomachs was examined, of which only 106 (23.7 percent) contained food. Stomachs of 572 specimens of fish, representing 9 species known to serve as food for gar, were obtained and the contents analyzed. Stomachs of fresh-water shrimp, Palaemonetes paludosa, and other invertebrates which entered into the food chains were examined. The diet of the gar consisted principally of fish although 57.5 percent of the stomachs contained shrimp and other invertebrates which comprised 23.6 percent of the total food volume. Four species of fish (bluegill, spotted sunfish, warmouth, and golden topminnow) eaten by gar were carnivorous; their diet was composed of invertebrates alone. Three species (redfin killifish, eastern mosquitofish, and least killifish) were omnivorous and consumed quantities of algae and invertebrates. Two species (sailfin molly and flagfish) were herbivorous, the stomach contents consisting primarily of algae and plant fragments. Algae and fragments of rooted vegetation made up the food of shrimp and most other invertebrates. The conversion of algae into gar involves only one or two intermediate steps. The two most important food chains are: (1) algae to herbivorous fish and herbivorous invertebrates to gar; (2) algae to herbivorous invertebrates to carnivorous fish and carnivorous invertebrates to gar. Zoo- and phytoplankton populations in the canal were small. Periphyton, the most common component of which was algae, was extremely abundant, covering all solid objects in the water with a soft slimy coat. The source of algae as the basic food for small fish and invertebrates was periphyton rather than phytoplankton.