"The temperature spikes can cause trouble for fish, plants and water quality".
"U.S. rivers are getting into hot water. The frequency of river and stream heat waves is on the rise, a new analysis shows.
Like marine heat waves, riverine heat waves occur when water temperatures creep above their typical range for five or more days (SN: 2/1/22). Using 26 years of United States Geological Survey data, researchers compiled daily temperatures for 70 sites in rivers and streams across the United States, and then calculated how many days each site experienced a heat wave per year. From 1996 to 2021, the annual average number of heat wave days per river climbed from 11 to 25, the team reports October 3 in Limnology and Oceanography Letters.
The study is the first assessment of heat waves in rivers across the country, says Spencer Tassone, an ecosystem ecologist at the University of Virginia in Charlottesville. He and his colleagues tallied nearly 4,000 heat wave events — jumping from 82 in 1996 to 198 in 2021 — and amounting to over 35,000 heat wave days. The researchers found that the frequency of extreme heat increased at sites above reservoirs and in free-flowing conditions but not below reservoirs — possibly because dams release cooler water downstream."