Environmental insults diminish an ecosystem's ability to maintain productive and adaptable populations of organisms. We have analyzed randomly amplified polymorphic DNA polymerase chain reaction (RAPD-PCR)-generated DNA profiles of naturally occurring rusty crayfish (Orconectes rusticus) populations from eight different populations collected from three separate sets of Ohio (USA) streams and find that changes in the underlying genetic diversity of these populations are significantly correlated (n = 144, p ≪ 0.001) with the extent to which they have been exposed to anthropogenic stressors. Because a population's genetic diversity is largely responsible for its vigor and ability to adapt to subsequent stressors, these results suggest that RAPD-PCR-based measures of genetic diversity may be suitable for development as a sensitive means of directly assessing the impact of stressors upon ecosystems.