New Map Identifies Most Resilient and Restorable Rivers in the US
Only six percent of all rivers and streams in the contiguous United States remain both in healthy ecological condition and meaningfully safeguarded against environmental degradation. That finding emerges from a comprehensive four-year assessment published September 16 in PLOS One, which maps one-third of the nation’s stream distances to guide conservation funding and ecological restoration as regional climates warm.
Key Clinical Takeaways:
- Researchers evaluated the lower 48 states’ waterways across four core metrics: network connectivity, floodplain and water quality, total water volume, and flow alteration.
- The assessment identified that 13 percent of the nation’s stream distances are currently in healthy condition but lack any formal legal safeguards or protection.
- More than half of the mapped stream distances qualify as either resilient or restorable, indicating that targeted interventions like dam removal can revive impaired aquatic habitats.
Mapping U.S. River Health and Watershed Resilience
For decades, environmental conservation initiatives across the United States have prioritized terrestrial ecosystems, systematically tracking intact forests and land ownership while freshwater networks received far less structural attention. To address this persistent blind spot, researchers from The Nature Conservancy and partners across 44 states evaluated waterways in diverse regions ranging from the humid East and arid Great Plains to Southwest deserts.
Each small watershed was graded on four specific criteria: network connectivity that allows fish and freshwater mussels to travel freely, floodplain condition and water quality, total water volume, and flow alterations driven by human activity. These watershed ratings were subsequently overlaid with 91 existing geospatial assessments detailing concentrations of native freshwater life.
“We can now point at a map for the first time and say, these are the rivers most capable of sustaining diversity of aquatic life, and this is what each one needs,” says Mary Khoury, a freshwater ecologist at The Nature Conservancy based in Chicago.
Geographic Distribution of Resilient and Vulnerable Waterways
The four-year analysis categorized rivers into distinct functional groups based on their capacity to sustain aquatic life under shifting climatic conditions. Waterways performing well across all four metrics were classified as resilient, while those scoring near average were deemed restorable—meaning they remain functional but are currently constrained by isolated environmental stressors such as agricultural runoff or obstructing infrastructure.
Healthy, resilient river systems cluster predominantly along the Pacific Coast, across the northern Rockies, and throughout the Southeast. Conversely, the most ecologically vulnerable river systems sit within the Southwest deserts, the Great Plains, and southern New England. Together, the resilient and restorable categories outline a comprehensive blueprint for maintaining freshwater biodiversity nationwide.
“A resilient system is one that gives species options and environments in which to adapt,” Khoury explains.
The Impact of Infrastructure and Unprotected Waterways
More than 150,000 dams currently fragment U.S. waterways, carving the nation’s river networks into over 9,000 separate, isolated segments that cut fish off from essential spawning grounds and cold-water refuges. The new mapping initiative pinpoints specific locations where reconnecting fragmented river segments would yield the highest ecological return on investment.
Among the primary examples of long, unbroken stretches within the resilient system are the Klamath River in Oregon and California—where lower barriers are currently undergoing the largest dam removal project in U.S. history—and the Delaware River, which flows unobstructed from New York’s Catskill Mountains to the Atlantic Ocean.
“I can see this being overlaid in the future, for example, with where dam licenses will expire, in order to find the most effective restoration opportunities,” notes Rafael Schmitt, a hydrologist at the University of California, Santa Barbara who was not involved in the study.
Unlike terrestrial conservation areas, where ecological health typically correlates strongly with formal protection status, river health displays a distinct vulnerability. The study revealed that 13 percent of the nation’s stream distances are in good ecological condition despite having no real regulatory safeguards. Because water flows continuously from upstream agricultural fields, subdivisions, and industrial sites into protected downstream segments, securing the long-term health of these unprotected aquatic ecosystems presents unique management challenges for environmental policymakers and local watershed protection specialists.