Development of a Comprehensive Instream Barrier Dataset for the Great Lakes Basin

A key challenge in regional and transboundary conservation decision making is identifying spatial datasets that are freely available at a similar resolution. This issue is particularly problematic for fresh waters, which commonly cross political boundaries. Instream barriers (e.g., dams, road crossings) have been identified as a restoration priority at regional and global scales, but spatial data on these barriers are lacking at these broader scales. We have begun addressing these data limitations for the Great Lakes Basin (GLB), which is one of the largest transboundary freshwater ecosystems. We compiled and refined existing spatial datasets on stream features and instream barriers that includes both large (>6 ft) and small dams, as well as the distribution of stream reaches and roads in the United States and Canada, and used these data to assess the occurrence of potential barriers to ecological connectivity across the entire basin. Using this refined dataset we found a five-fold increase in the number of georeferenced dams compared to the National Inventory of Dams, which is the most comprehensive dataset currently available for decision making that crosses state boundaries in the GLB. Our analyses also identified over 269 000 road-stream crossings that could act as barriers. The datasets we have developed are seamless across political boundaries, are based on hydrography and roads mapped at a consistent scale, and will help facilitate prioritization of barrier removal across the entire basin.