Mercury levels of largemouth bass from three reservoirs in the southeastern United States were highest in the younger, relatively oligotrophic reservoirs and were significantly lower in an older, more eutrophic reservoir in the same drainage system. The reservoir with the highest mercury levels in bass is the reservoir farthest upstream, and is not subject to inputs of municipal or industral wastes. The source of mercury in these reservoirs appears to be the soil which formed theri original sediments. Preliminary data indicate that mercury levels in largemouth bass in these systems decline as the reservoirs age. televated mercury levels in fish appear to be a transitory phenomenon in newly impounded, relatively oligotrophic reservoirs.