Our Rivers Are Suffering From Surging Heat Waves

It's not just the oceans that are warming. America's rivers are heating up at a record pace, with new research revealing that stream heat waves are growing more frequent and intense—posing risks to aquatic life adapted to cooler waters. A new study analyzing more than 40 years of temperature data from nearly 1,500 river sites found that river heat waves are becoming more frequent, more intense, and longer-lasting, per NBC News. According to the research, published Monday in the Proceedings of the National Academy of Sciences, these riverine heat waves—defined as five consecutive days above average temperatures—are increasing at two to four times the rate of air heat waves, per New Atlas.

Human-driven climate change is cited as the primary culprit, with dwindling snowpacks and slower stream flows, partly due to dams, contributing to the trend. Added to that, buildings and pavement absorb heat, warming the air and river waters. This spells trouble for cold-water species like salmon and trout, which face mounting stress as higher water temperatures reduce dissolved oxygen and raise metabolic demands.

The study's data shows the average river now experiences nearly two more heat wave events per year than it did in 1980. These events are also more severe, with heat wave temperatures nearly one degree Fahrenheit higher and lasting over three days longer than in the past. On average, species that require cold water are now facing about 12 additional days of heat stress annually, per NBC. While heat waves in oceans and lakes have been widely studied, rivers have lagged due to patchier monitoring. The findings highlight the need for new approaches to water management, such as strategic dam releases, to help vulnerable species cope.