The pollution of lakes on golf courses from mercurial fungicides used in greens treatment was studied. Golf courses near Columbia, Kansas City, St. Louis, and New Bloomfield, Mo., were selected for study. Several species of fish as well as water, algae, and bottom sediments samples were collected from each lake. Mercury was determined by a flameless atomic absorption method. The results indicate that there can be significant pollution of lakes on golf courses from the greens treatment, especially if organically bound mercury is used in the treatment. The flesh of mature largemouth bass was the most sensitive indicator. Many lakes with no known source of mercury contamination produce mature bass which contain significantly more mercury than the 0.5 ppm recommended by the FDA as the maximum for human food.