To assess mercury contamination of fish in Maine, fish were collected from 120 randomly selected lakes. The collection goal for each lake was five fish of the single most common sport fish species within the size range commonly harvested by anglers. Skinless, boneless fillets of fish from each lake were composited, homogenized, and analyzed for total mercury. The two most abundant species, brook troutSalvelinus fontinalisand smallmouth bassMicropterus dolomieu, were also analyzed individually. The composite fish analyses indicate high concentrations of mercury, particularly in large and long-lived nonsalmonid species. Chain pickerelEsox niger, smallmouth bass, largemouth bassMicropterus salmoides, and white perchMorone americanahad the highest average mercury concentrations, and brook trout and yellow perchPerca flavescenshad the lowest. The mean species composite mercury concentration was positively correlated with a factor incorporating the average size and age of the fish. Lakes containing fish with high mercury concentrations were not clustered near known industrial or population centers but were commonest in the area within 150 km of the seacoast, reflecting the geographical distribution of species that contained higher mercury concentrations. Stocked and wild brook trout were not different in length or weight, but wild fish were older and had higher mercury concentrations. Fish populations maintained by frequent introductions of hatchery-produced fish and subject to high angler exploitation rates may consist of younger fish with lower exposure to environmental mercury and thus contain lower concentrations than wild populations.