The Salmonella typhimurium/mammalian microsome test has provided a simple and sensitive short‐term assay for the detection of environmental mutagens. Metabolic activation of precarcinogens is usually achieved by incubating the compound to be tested, the bacterial strain and mammalian liver homogenates with NADPH. The results presented here utilize Salmonella typhimurium strain TA100, the precarcinogen 2‐aminofluorene and microsomal enzyme preparations prepared from liver homogenate of carp (Cyprinus carpio) taken from aquatic environments of northeastern Tennessee. Those environments range from virtually unpolluted to extremely polluted. The results show that the precarcinogen 2‐aminofluorene is activated either partially or totally in the presence of liver homogenates of carp taken from polluted aquatic environments (e.g., microsomal enzyme preparations made from rat liver with 2‐aminofluorene produced 808 revertants; whereas the liver preparations made from carp, taken from the Pigeon River, with 2‐aminofluorene produced 2,786 revertants). Revertant colony results correlated well with the degree of pollution within those waters. An increase (data were statistically different at the 0.05 level of significance) of TA100 revertant colonies was observed as aquatic contamination worsened. All data pairs of collecting sites in their order of increasing contamination, as well as those between collecting sites, were statistically different at the 0.05 level of significance.