Dams can exert great influence on fluvial habitats through a variety of mechanisms, however spatial measures representing dam locations throughout river networks, along with their attributes (e.g. reservoir storage), are not available in a consistent, comparable manner for the conterminous U.S. In this study, spatial metrics are developed that account for fragmentation and alteration of river networks by large dams throughout the conterminous U.S., allowing for the examination of river network fragmentation patterns by stream size and ecoregion. Results show that streams in the conterminous U.S. have been heavily fragmented by dams, with the greatest dam influence tending to occur in large and great rivers due to cumulative dam effects along river networks. Using a subset of fragmentation metrics generated in this study, fish species considered to be most sensitive to dam influences were identified for streams in Michigan, Wisconsin, and Minnesota. Of the sensitive species identified, those that were positively associated with greater dam effects were predominantly fishes associated with warm water temperatures, large river habitats, and/or lentic habitats, while species negatively associated with greater dam effects were cold and coolwater lotic species, suggesting a combination of downstream thermal effects and upstream influences from impoundments generated by dams. With dams representing an aging infrastructure leading to likely increases in habitat restoration and dam management opportunities, it will be essential to further reveal the spatial influence of dams along the river network.
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