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Pollution is a threat to lotic fishes that enter streams via point source (PS) and nonpoint source (NPS) pathways. The Clean Water Act (CWA) of 1972 and the Surface Mining Control and Reclamation Act (SMCRA) of 1977 reduced PS pollution in the United States, but little information is available concerning the response of fish communities to this legislation. The objectives of this research were to quantify the responses of fishes to the CWA and SMCRA in the Cow Creek watershed of southeastern Kansas, a wadeable stream network that experienced large reductions in PS pollution. Responses were quantified by measuring changes in site occupancy, relative abundance, and species richness across 25 sites sampled in 1963 and again in 2017. Responses were compared among fishes that were intolerant, moderately intolerant, moderately tolerant, and tolerant of pollution using an analysis of deviance coupled with general linear hypothesis testing. We predicted that intolerant fishes would exhibit the most dramatic increases in distribution and abundance and that these changes would be most evident in streams that were directly receiving PS pollution in 1963. However, our predictions were not met, as species tolerant of pollution exhibited greater occupancy, relative abundance, and richness than did intolerant fishes, regardless of time period. Contemporary pH and substrate composition were also quantified and revealed that most streams had recovered from historical acid mine drainage but were dominated by fine substrates. We hypothesized that the limited responses exhibited by intolerant fishes were at least partially attributable to NPS pollution (i.e., sedimentation) resulting from agriculture, which was the dominant land use both historically and currently. We conclude that reductions in both NPS pollution coupled with historical reductions in PS pollution may be necessary to increase the prevalence of intolerant fishes. These management actions may have conservation implications as many intolerant fishes are also imperiled.

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