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Visitors heading to Yellowstone National Park this summer will find some of the park’s best-known fishing rivers closed due to extreme water temperatures.
In a July 15 announcement, National Park Service (NPS) officials from Yellowstone said the Madison, Firehole and Gibbon rivers would be temporarily closed to fishing until further notice.
The affected rivers are all located on Yellowstone’s west and northwest sides, near some of the park’s busiest attractions, and the Firehole River flows through the Old Faithful area.
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The closures are in effect 24 hours a day. Officials blamed unusually warm water temperatures, which can be lethal to Yellowstone’s famed trout.
“In recent days, peak water temperatures have ranged from 80 to 86 degrees Fahrenheit during the day,” the notice said.
“Coupled with high air temperatures, these conditions are lethal to trout, and there have been reports of dead fish in the Firehole River.”
Officials added there are currently no heat-related fishing restrictions on other lakes, rivers or streams in the park.
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The temporary closures will “protect the park’s native and wild trout fisheries and will remain in effect until conditions improve,” according to the NPS.
Trout struggle to survive in exceptionally warm water because their bodies warm along with their surroundings, said Steven J. Cooke, a biology professor at Carleton University in Canada.
“Fish are ectotherms, which means that their body temperature is the same as the water temperature,” Cooke told Fox News Digital.
“At high temperatures, trout struggle to obtain enough oxygen and may not recover upon release.”
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Cooke, based in Ottawa, Ontario, added that anglers “need to get used to such closures, as they will become more common.”
Anglers “need to get used to such closures, as they will become more common.”
“However, if anglers up their game and improve their fish handling by minimizing fight time and eliminating air exposure, then that will be better for fish and allow continued fishing,” he said.
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“We are seeing the same thing play out with muskellunge anglers in the Midwest, or Atlantic salmon anglers in the Northeast.”
Cooke, who is on the board of the nonprofit organization Keep Fish Wet, said regulations like fishing closures “make more sense” in national parks, to ensure sensitive resources are protected.
Keep Fish Wet educates anglers on science-based best practices for catch-and-release fishing to maximize fish survival rates.
According to the NPS’s website, Yellowstone has long been a popular destination for anglers.
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“Yellowstone supports some of the world’s most famous fisheries and has been a destination for generations of anglers for over 150 years,” the site states.
“Fishing regulations are designed to maintain native fish abundance and genetic integrity, the park’s overall ecological integrity, and a recreational fishery for park visitors.”
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Fox News Digital reached out to the NPS for comment.