Ecological condition of mountain lakes in the conterminous United States and vulnerability to human development

Mountain lakes are sentinel ecosystems that provide unique ecological habitat and natural resources with high cultural and recreational value to communities globally. Despite their recognized importance, there is no consistent definition of what constitutes a mountain lake, and this hampers the study of these systems as a population. In this study, we develop a rules-based approach for classifying mountain lakes according to catchment topography. We apply the approach to lakes surveyed in the United States National Lakes Assessment, which includes the population of lakes that are at least 1 ha in surface area and 1 m deep, to evaluate the condition of mountain lakes across the conterminous US (CONUS). We found there are an estimated 12,353 (95% C.I. 10,529–14,177) mountain lakes that accounts for 6.4% of the lake population in the CONUS. Mountain lakes were in better condition than non-mountain lakes for 10 of 11 physical, chemical, and biological indicators. However, a notable proportion of mountain lakes are in fair or poor condition for specific indicators. For instance, approximately 25% of mountain lakes are classified as eutrophic or hypereutrophic, and nearly 50% were in fair or poor condition with respect to riparian vegetation and lakeshore disturbance. There is a lower proportion of developed lands overall in mountain lake watersheds, but development patterns are concentrated along the lakeshore and thus may have a disproportionate impact. This, coupled with characteristics such as high runoff, low hydraulic conductivity, and shallow bedrock depths, may render mountain lakes increasingly susceptible to the adverse effects of human development and climate change compared to non-mountain lakes. These findings underscore the need for targeted conservation and management strategies to protect ecologically sensitive lake environments.

Impact/Purpose

This manuscript is based on an analysis that was conducted in response to a request from congress about the status and threats to alpine lakes. An analysis leveraging existing data was prepared and sent back to congress as a briefing document. The request and resulting briefing motivated the team to expand and refine the analysis in order to speak to mountain lakes across the US. Alpine lakes a generally defined as occurring above 10,000 ft in elevation. This definition excludes many mountain lakes that are of cultural significance and have high recreational value. We developed a rules-based framework for identifying these lakes and apply it to the EPA's National Lakes Assessment. The analysis found that mountain lakes can occur in a wide range of elevations across the conterminous US and that mountain lakes are in better physical, chemical, and biological condition than non-mountain lakes with respect to ten key indicators. However, we also found that mountain lakes have development concentration along the lakeshore and thus have disproportionate impact. These findings underscore the need for targeted conservation and management strategies to protect ecologically sensitive lake environments.

Citation

Handler, A., M. Weber, M. Dumelle, L. Jansen, Jim Carleton, B. Schaeffer, S. Paulsen, T. Barnum, A. Rea, A. Neale, AND J. Compton. Ecological condition of mountain lakes in the conterminous United States and vulnerability to human development. Elsevier Science Ltd, New York, NY, 173:113402, (2025). [DOI: 10.1016/j.ecolind.2025.113402]

DOI: Ecological condition of mountain lakes in the conterminous United States and vulnerability to human development