Protecting a Third of US Rivers Could Save Freshwater Species, Study Finds

Freshwater ecosystems are quietly collapsing across the United States, and a sweeping new analysis suggests there is still a realistic path to stopping the decline. In a study published on September 16, 2026 in the open-access journal PLOS One, a team led by Mark Anderson of The Nature Conservancy mapped the resilience and connectivity of rivers and streams throughout the contiguous United States and arrived at a striking conclusion: conserving and restoring roughly 35 percent of the nation’s waterways could be enough to sustain the country’s freshwater biodiversity even as habitat degradation and climate change intensify. The finding reframes what can feel like an overwhelming conservation problem into a targeted, spatially explicit strategy, identifying precisely which rivers and streams offer the greatest chance of preserving aquatic life into an uncertain future.

The scale of the problem the study confronts is difficult to overstate. Over the past century, streams and lakes across the country have deteriorated under mounting human pressure. More than 150,000 dams now fragment river networks, severing the upstream and downstream connections that countless species depend on for migration, spawning and genetic exchange. Beyond the barriers themselves, changes to the landscape, from agriculture to urbanization, and the extraction of groundwater have altered how and where water flows through entire watersheds. Flow regimes that evolved over millennia have been reshaped within a few human generations, and the consequences are visible in the biological record. Many freshwater species are now in rapid decline, a trend that researchers warn is being exacerbated by the impacts of a changing climate, which shifts temperature and precipitation patterns faster than aquatic organisms can disperse or adapt.

To confront this crisis systematically, The Nature Conservancy assembled a collaboration of 66 freshwater conservationists and set out to map freshwater networks across the contiguous United States and evaluate how resilient each one is to degradation. The approach was deliberately multidimensional. Each watershed received scores based on four criteria: its connectivity, meaning how well its aquatic habitats link together into functioning networks; its condition, reflecting the ecological integrity of the stream or river; its water availability; and the naturalness of its flow, a measure of how closely the timing and magnitude of water movement still resemble historical patterns. These scores were then checked against local surveys of freshwater biodiversity, grounding the resilience assessment in observed biological reality rather than purely physical or chemical proxies.

The result of this effort is a spatial blueprint the researchers call the Freshwater Resilient and Connected Network. This patchwork of rivers and streams covers 35 percent of the lower 48 states, yet the analysis indicates it could preserve the nation’s freshwater biodiversity if conserved and, where necessary, restored. The logic behind such a network is rooted in conservation biology: rather than spreading limited resources thinly across every waterway, concentrating protection on the places where ecosystems are most intact, most connected and most likely to withstand climatic disruption offers a disproportionate return on investment. Resilient, connected networks give species room to move, access to diverse habitat types and the ecological redundancy needed to absorb disturbances such as droughts, floods and warming waters.

Realizing that vision, however, will be a formidable challenge, and the study is candid about the gap between ambition and current reality. Of the 35 percent of waterways identified in the network, only 6 percent of the area is both protected and resilient today. A further 14 percent needs both protection and restoration before it can fulfill its role in the network. In other words, the vast majority of the lands and waters that underpin the nation’s freshwater future currently lack formal safeguards, and many have already been degraded enough to require active intervention. The numbers underscore that identifying priority areas is only the first step; the harder work of securing durable protection and reversing damage on the ground remains ahead.

The broader statistical picture the analysis paints of the contiguous United States is equally revealing. Of the 5.2 million miles of rivers and streams in the lower 48 states, 33 percent rated as above average for resilience. Rivers in this category should continue to support similar patterns of biodiversity in the future, making them strong candidates for protection. The researchers note an important nuance, however: rivers that score just above average may still require restoration to maintain their ecological function, meaning that even some of the better-performing waterways cannot simply be left alone. The geography of resilience is uneven as well. The strongest networks are concentrated along the Pacific Coast, in the Northern Rocky Mountains, around the Great Lake areas of Wisconsin and Minnesota, in northern Maine, and along the coastal regions of the southeastern United States and the Gulf of Mexico, areas where relatively intact landscapes and healthier flow regimes persist.

At the other end of the spectrum, vulnerable or below-average river networks made up 15 percent of the nation’s river and stream miles, and their distribution tells a story about the cumulative weight of human land use and arid climates. These stressed networks cluster in the Southwest deserts, in lower New England, across the shortgrass prairie east of the Rocky Mountains, and throughout the agricultural lands of the midwestern states. In these regions, decades of water diversion, damming, row-crop cultivation and development have eroded the connectivity and natural flow patterns that freshwater communities need. The identification of these hotspots of vulnerability is not merely descriptive; it signals where restoration investment is most urgent if the country hopes to prevent further local extinctions and the loss of aquatic ecosystem services.

The practical value of the new maps is already being demonstrated, according to the research team. The analysis has been used to identify dams for removal, a critical step in reestablishing longitudinal connectivity in fragmented river systems. It has also guided the prioritization of land protection in key headwaters, where safeguarding the upper reaches of watersheds protects water quality and flow for everything downstream. In addition, the framework is being applied to improve conditions in river systems that need restoration, directing effort toward reaches where interventions are most likely to succeed. The authors acknowledge one important limitation: the maps do not take into account human needs, such as water supply, recreation and economic uses of rivers. They note, however, that data representing human dimensions could be combined with this analysis to identify where conservation goals and human priorities intersect or conflict.

The researchers emphasize that resilience to climate change adds essential context to biodiversity conservation that static protection alone cannot provide. A reserve that protects a species’ current habitat may fail within decades if warming, altered precipitation or shifting flow regimes render that habitat unsuitable. By scoring watersheds for the physical features that confer long-term resilience, such as connectedness, water availability and natural flow, the framework aims to identify places where biodiversity can persist not just today but across a range of future climate scenarios. The authors state the hope directly: resilience to climate changes adds important context to efforts to conserve freshwater biodiversity, and they hope the study will help state, federal, Tribal and other conservation partners make investments where they have the greatest chance to succeed into the future.

The study, authored by Mark G. Anderson, Arlene P. Olivero, Analie R. Barnett, Melissa L. Khoury and Erika H. Martin of The Nature Conservancy, was funded by an anonymous donor, the Volgenau Foundation, Kia America and the Enterprise Mobility Fund, none of which played a role in study design, data collection and analysis, decision to publish or manuscript preparation. The authors report no known competing interests. As an observational, nationwide assessment published in PLOS One, it offers conservation planners a rigorous, data-driven foundation for sustaining freshwater life across the United States, and a clear-eyed picture of the challenges ahead: a third of the nation’s waters hold the key, but most of that territory still awaits the protection and restoration it will need to do its job.

Subject of Research: Mapping resilient and connected freshwater networks to conserve biodiversity in United States rivers and streams under climate change

Article Title: Conserving just 35% of nation’s waterways could sustain freshwater biodiversity

Article References: Conserving just 35% of nation’s waterways could sustain freshwater biodiversity. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: freshwater biodiversity, river conservation, climate resilience, PLOS One, The Nature Conservancy, watershed connectivity, dam removal, stream restoration, United States rivers, habitat protection, flow regime, conservation planning