U.S. rivers are experiencing unprecedented and unexpectedly intense warming [View all]

Source: NBC News

Sept. 22, 2025, 5:27 PM EDT


U.S. rivers are running hot.

A new analysis of nearly 1,500 river locations over more than 40 years found that the frequency, intensity and duration of heat waves is increasing in streams across the country, posing a threat to many species that are adapted to cooler temperatures.

“The trend of river heat waves is actually increasing faster than the air heat waves. So, that’s one thing that is very surprising,” said Li Li, a professor of environmental engineering at Penn State University and an author of the study.

The new analysis, which was published in the peer-reviewed journal Proceedings of the National Academy of Sciences, is the first in-depth study of riverine heat waves, which are defined as five straight days of high temperatures in comparison to seasonal averages.

Read more: https://www.nbcnews.com/science/climate-change/us-rivers-are-experiencing-unprecedented-unexpectedly-intense-warming-rcna233002