Rating US reservoirs relative to fish habitat condition

Fish habitats in many aging US reservoirs have become degraded and require broad-scale assessment to rate their status and facilitate rehabilitation efforts. To help prioritize habitat projects in reservoirs, we assembled a rating system for large reservoirs in the contiguous United States. Using responses to an online questionnaire about fish habitat impairment in 1299 large US reservoirs, we applied multivariate analyses to identify combinations of habitat impairment descriptors that quantified broad impairment types (i.e., a construct). Resulting constructs reflected point source pollution, nonpoint source pollution, excessive nutrients, algae blooms, siltation, limited nutrients, mudflats and shallowness, limited connectivity to adjacent habitats, limited littoral structure, nuisance species, anomalous water regimes, and large water level fluctuations. Scores were summed across constructs to create a composite number that rated overall reservoir habitat impairment. Construct and composite scores differed among geographic ecoregions of the United States. This rating system could provide a starting point for prioritizing reservoirs for habitat rehabilitation and enhancement projects.