River connectivity increases the diversity of fish communities in gravel pit lakes.

Objective: Off‐channel floodplain features are important components of a river system that provide habitat and boost regional species pools, but river–floodplain connectivity is disrupted by anthropogenic activities. The Campbell Lakes in Harrison, Ohio, are formerly isolated gravel pits along the Whitewater River and are connected to the river through flooding‐related erosion. The lakes were first stocked with sport fish by Great Parks of Hamilton County to promote recreational fishing, but stocking ended in 2019 due to frequent connection with the Whitewater River during high flow. We explored how the fish community composition of the Campbell Lakes reflects increasing connectivity with the Whitewater River and among the lakes. Methods: Using historical aerial photographs and river discharge estimates, we established an approximate timeline of permanent connectivity and potential breaches between the lakes and the Whitewater River from 2000 to 2020. Fish community data collected via electrofishing surveys of the Campbell Lakes in 2004, 2007, 2012, and 2020 were compared to data from surveys of the Whitewater and Great Miami rivers in 1995 and 2013. Result: The lakes were dominated by centrarchid species in early surveys but showed increased species and family richness with time. Based on an analysis of similarity and nonmetric multidimensional scaling, the lakes' fish communities differed significantly among years and gradually increased in resemblance to the river communities. Conclusion: Our results suggest that the Campbell Lakes fish communities are broadening to include taxa from the Whitewater and Great Miami River communities and are shifting from lentic to lotic species. The change in fish community assemblages in the Campbell Lakes demonstrates the potential for gravel pit lakes to serve as artificial floodplain features that can enhance river–floodplain connectivity. Impact StatementAs four gravel pit lakes became increasingly connected with an adjacent river through temporary flooding and permanent channels, fish community assemblages in the lakes diversified and transitioned from stocked lentic species to riverine backwater species. Gravel pit lakes can act as oxbow lakes to provide additional floodplain habitat for riverine species. [ABSTRACT FROM AUTHOR]