Heat wave sets record temps in Potomac River, contributing to large fish kill

Name: Potomac River sets record temperature during blistering heat wave, contributing to large fish kill
Uploaded: 2026-07-09T13:34:16-04:00
Duration: 40 s
Description: The East Coast's Fourth of July heat wave drove the Potomac River north of Little Falls, Maryland, to a record temperature, contributing to a large fish kill, officials said. The Maryland Department of the Environment said one of its biologists recorded a water temperature of 94 degrees on July 4, while data from the USGS shows water temperatures peaking at 98.4 degrees.

The East Coast's Fourth of July heat wave drove the Potomac River north of Little Falls, Maryland, to a record temperature, contributing to a large fish kill, officials said. The Maryland Department of the Environment said one of its biologists recorded a water temperature of 94 degrees on July 4, while data from the USGS shows water temperatures peaking at 98.4 degrees.

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Potomac River sets record temperature during blistering heat wave, contributing to large fish kill

The East Coast's Fourth of July heat wave drove the Potomac River north of Little Falls, Maryland, to a record temperature, contributing to a large fish kill, officials said. The Maryland Department of the Environment said one of its biologists recorded a water temperature of 94 degrees on July 4, while data from the USGS shows water temperatures peaking at 98.4 degrees.

LITTLE FALLS, Md. — The East Coast's Fourth of July heat wave drove the Potomac River north of Little Falls, Maryland, to a record temperature, contributing to a large fish kill, officials said.

The Maryland Department of the Environment said one of its biologists recorded a water temperature of 94 degrees on July 4, while data from the USGS shows water temperatures peaking at 98.4 degrees.

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OAKLAND, CA - AUGUST 30: Ten thousands of dead fish piled up around the Lake Merritt of Oakland after suffocating due to toxic algae in San Francisco Bay, California, United States on August 30, 2022. (Photo by Tayfun Coskun/Anadolu Agency via Getty Images) (Photo by Tayfun Coskun/Anadolu Agency via Getty Images))

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OAKLAND, CALIFORNIA - AUGUST 30: In an aerial view, hundreds of dead fish are seen floating in the waters of Lake Merritt, a tidal lagoon of the San Francisco Bay, on August 30, 2022 in Oakland, California. Tens of thousands of dead fish, including sharks, sturgeon and large striped bass, are showing up on the shores of the San Francisco Bay and its waterways as a widespread algal bloom continues more than a month after first being detected. The algae is not believed to be immediately harmful to humans but could be fatal to fish and other marine life if exposed in high concentrations. (Photo by Justin Sullivan/Getty Images) ((Photo by Justin Sullivan/Getty Images))

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Red tide fish kill along the Florida coast (USF)

According to the FOX Forecast Center, this is the warmest temperature ever recorded since record keeping began at this site in 1988.

Officials said the fish kill spanned nearly 14 miles between Whites’s Ferry and Violette’s Lock in Montgomery County.

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Most of the fish found were golden redhorse suckers. Scientists said extreme water temperatures created stressful conditions for the fish and was a primary reason for the large number of deaths.

Warmer water holds less dissolved oxygen, leaving less oxygen available for fish.

Historic heat wave roasts Washington, D.C.

(FOX Weather / FOX Weather)

The department said there was no evidence of a chemical spill or pollution in the area of this kill.

That came amid three straight days of record-high temperatures in nearby Washington, D.C., including a new Independence Day record of 103 degrees. New Jersey health officials told FOX Weather that at least 29 deaths across several counties have been preliminarily linked to the extreme temperatures.