Thursday October 1, 2026
Science News —
First, the bad news: Of all the rivers in the contiguous United States, only 6 percent are both in healthy condition and meaningfully safeguarded. The good news is that many more may be just one repair away from thriving.
A new map highlights where conservation money and attention would do the most good as the climate warms, researchers report September 16 in PLOS One. The effort is the most comprehensive to date, assessing the health of the lower 48 states’ rivers and streams.
“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 who is based in Chicago.
For decades, conservation in the United States has been organized primarily around land. Scientists know for the most part which forests are intact and who owns what. Rivers have never gotten that treatment, even as more than 150,000 dams have fragmented the country’s waterways — cutting fish off from spawning grounds and cold-water refuges — and climate change has altered the temperatures and flows these animals depend on.
The new assessment, which took four years, maps one-third of the nation’s stream distances. Each small watershed was rated on four measures: how connected its river network is, meaning whether animals including fish and mussels can freely travel along it; the condition of its floodplain and water quality; how much water it has; and how much its flows have been altered. Those ratings were laid over 91 existing assessments of where freshwater life is concentrated. Dozens of scientists and partners from 44 states adjusted the measures for river systems in regions as different as the humid East, the arid Great Plains and the deserts of the Southwest.