Shallow waters off south Florida topped 100 degrees Fahrenheit (37.8C) for several hours on Monday, potentially setting a new world record with temperatures more commonly associated with hot tubs.
The readings were taken from a single buoy in Manatee Bay, about 38 miles (60 kilometers) southwest of Miami, at a depth of five feet (1.5 meters).
A peak temperature of 101.1F was recorded at 6:00 pm, but it remained above 100F for about four hours, official data showed.
Jeff Masters, a meteorologist and former government scientist, tweeted that while there was no official world record for sea surface temperature, a 2020 scientific paper found that the previous high might have been 99.7F recorded in Kuwait Bay.
But, added Masters, since the new measurement was taken near land, "contamination of the measurement by land effects and organic matter in the water might…invalidate the record."
"Unless there is photographic proof that debris was not present, it would be difficult to (verify) the 101.F record as valid," he added on social media.
The sauna-like conditions might be enjoyable for some humans, but sustained extreme heat is devastating for coral reef ecosystems and the species that depend on them.
It comes days after the nonprofit Coral Restoration Foundation (CRF) said that one reef in south Florida it had been working to restore had been devastated.
"CRF teams visited Sombrero Reef, a restoration site we've been working at for over a decade. What we found was unimaginable – 100 percent coral mortality," said the organization's Phanor Montoya-Maya, in a statement.
About 25 percent of all marine species are found in, on, or around coral reefs, rivaling the biodiversity of tropical rainforests, according to the US National Oceanic and Atmospheric Administration.
Across the globe, the Mediterranean Sea reached its highest temperature on record Monday during an exceptional heatwave, Spanish researchers told AFP on Tuesday.
"We attained a new record… in the daily median sea surface temperature of the Mediterranean: 28.71C (83.68F)," Spain's Institute of Marine Sciences said.
The previous record was on 23 August 2003, with a median value of 82.86F.
July 2023 is on track to be the hottest absolute month on record, as well as the hottest in potentially thousands of years, according to NASA climatologist Gavin Schmidt.