The Wildlife Conservation Society (WCS) and the Center for International Earth Science Information Network (CIESIN) have quantified human impacts on the natural environment through their Human Footprint dataset. Human Footprint incorporates three themes: population pressure, land use with infrastructure, and human access. For our analysis, we averaged human footprint values over each ecoregion. We acknowledge some limitations of using this dataset to assess threats to freshwater systems. For example, in the Human Footprint calculation navigable rivers are identified as allowing access to otherwise remote regions and are therefore highlighted as areas of higher impact. While greater human activity in a region will likely lead to greater impacts on freshwaters, those impacts may differ markedly depending on the type of human activity and the type of river use. Nonetheless, we present Human Footprint by ecoregion as a coarse indicator of the extent of human activity that may affect freshwaters.