Mercury contamination levels were studied in several species of waterfowl wintering on a reactor cooling reservoir (Par Pond) of the u.s. Department of Energy's (U .S. D.O.E.) Savannah River Plant near Aiken, South Carolina. Samples from 177 American coots (Fulica americana) indicated that this species which is largely vegetarian on its wintering grounds, had lower levels of mercury accumulation than did 4 other aquatic species which were more carnivorous in their food habits. Coot feathers had the highest frequency (88.1 %) of detectable levels of mercury, and gut contents had the lowest (0.2%). Mercury in coot feather samples was not affected by month of collection or location within the reservoir. The highest frequency of mercury in breast muscle occurred in the first birds to arrive in early fall. Frequencies of mercury contamination in breast muscle then tended to decline generally throughout the remainder of the fall, winter and spring. Radiocesium cycling patterns were useful in interpreting monthly changes in mercury contamination of Par Pond coots, despite differences in both temporal and spatial cycling patterns of these contaminants in the resident waterfowl community.