Only 6 percent of rivers in the contiguous United States are both ecologically healthy and formally protected, according to a comprehensive four-year assessment published in PLOS One on September 16, 2026. While this indicates that a small fraction of waterways currently enjoy meaningful safeguards, researchers have developed a new map to identify where future conservation efforts and funding could be most effective as the climate warms.
The study, which examined one-third of the nation’s stream distances, categorized rivers based on four key measures: network connectivity, floodplain condition, water quality, and flow integrity. These findings were cross-referenced with 91 existing assessments regarding the concentration of freshwater life. The results offer a roadmap for prioritizing environmental interventions, distinguishing between systems that are already resilient and those that could be restored to health through specific actions, such as addressing farm runoff or removing obstructing dams.
Identifying Resilient and Restorable Waters
The assessment found that more than half of the mapped stream distances qualify as resilient, meaning they perform well across all four evaluation criteria. Rivers that do not meet these high standards were classified as restorable. These systems remain functional but are limited by singular issues that, if corrected, could allow the rivers to thrive. Collectively, these two categories form what researchers describe as a freshwater resilient and connected network.
Geographically, the healthiest rivers are concentrated along the Pacific Coast, across the Southeast, and in the northern Rockies. Conversely, the most vulnerable waterways are located in the Great Plains, southern New England, and the deserts of the Southwest.
Addressing Fragmentation and Protection Gaps
A primary challenge for U.S. waterways is fragmentation, with more than 150,000 dams dividing rivers into over 9,000 separate pieces. This prevents fish and mussels from accessing spawning grounds and cold-water refuges. The new data highlights areas where reconnecting these systems would provide the greatest benefit to aquatic diversity. Notably, the study identifies long, unbroken stretches such as the Delaware River and the Klamath River as key components of the resilient network.
The research also highlights a discrepancy between ecological health and formal protection. Unlike land-based conservation, where the healthiest areas are typically the most protected, the study found that 13 percent of the country’s stream distances are in good condition but lack any real safeguards. According to Mary Khoury, a freshwater ecologist at The Nature Conservancy, the map provides a tool to ensure that conservation efforts focus on systems that offer species the best environments in which to adapt.
