Making Waves: The Effects of Whitewater Parks on Fish Passage in Colorado

ABSTRACT Instream structures have fragmented riverine habitats throughout much of the world, including the Western USA. Whitewater parks (WWPs) are relatively new instream structures designed to create hydraulic waves for recreational boating and surfing by constricting flows into a steep chute or drop. The altered hydraulics at these structures can adversely affect fish passage, particularly in locations where fish species are not adapted to the new hydraulic regime. This study evaluates the effects of WWPs on fish passage at two sites in Colorado by comparing water velocity and depth to fish passage criteria for three size classes (juvenile, average adult, and large adult) and species of interest (Brown Trout, Colorado Sculpin, and Flannelmouth Sucker). The before‐after study design utilized two‐dimensional hydrodynamic modeling, spatial analysis, and logistic regression to evaluate fish passage over a range of flows. WWP construction altered channel hydraulics, including elevated and more variable velocity, and decreased depth. Complete barriers to upstream passage were created for certain combinations of species, size class, and flows due to velocity and/or depth limitations. Passable pathways and passage probability decreased for all species following WWP construction, with Brown Trout maintaining the highest proportion of passable paths (23%) when averaged across flows and structure, followed by Colorado Sculpin (15%) and Flannelmouth Sucker (2%). These results indicate that WWP construction decreased fish passage at these sites and highlight the importance of using site‐specific criteria and permitting requirements to ensure that adequate safeguards for fish passage are incorporated into the design of WWP structures.