Water quality improvements correspond with increased human use and occurrence of fish, aquatic insects, and freshwater mussels

Seth A. Drake, Lindsey A. Bruckerhoff, Robert Miltner, Nathaniel F. Shoobs, Casey A. Pennock. Ecological Indicators. Volume 188, July 2026, 115034. DOI: 10.1016/j.ecolind.2026.115034.

Abstract

Documenting species responses to ecosystem level policy and conservation actions is critical to slow or reverse the global biodiversity crisis. We quantified changes in water quality, fish and insect assemblages (1978–2023), and freshwater mussels (1970–2023) over time associated with implementation of broad environmental regulations including the Clean Water Act, Clean Air Act and other best management practices across seven major river basins in the state of Ohio, USA. Water quality improvements were characterized by declines in zinc, nitrite, and lead across the state, and declines in ammonia and total phosphorus in most river basins. Occurrences of fish and insect species classified as intolerant to poor water quality increased across river basins, especially in large rivers. Seventy-one fish species and 171 insect taxa increased in occurrence and few species decreased. However, freshwater mussels had mixed responses over time, with 9 species increasing and 10 decreasing in occurrence, indicating the need for continued water quality improvements and potentially conservation efforts to repatriate mussels with low dispersal capabilities. This study documents long-term improvements in water quality and increased occurrence of aquatic species that are likely associated with environmental regulations and best management practices. Our results highlight the need for regulations to remain in place to maintain conservation gains for fishes and insects and potentially expanded regulations to facilitate gains for freshwater mussels. These results are critically important as the US federal government reconsiders implementation of environmental policy and funding of agencies enforcing environmental regulations.