Thursday's median temperature was, according to the Institute of Marine Sciences in Barcelona, 28.90 degrees, compared to the previous record of 28.71 degrees from July 2023.
The warmest was the sea off Egypt's northeastern coast, where the surface water measured 31.96 degrees according to preliminary figures. The figures come from satellite data collected by the EU's observation system Copernicus.
Before last year's heatwave, the previous record had stood since 2003.
The high temperatures risk, according to researchers, threatening the marine animal and plant life. During previous heatwaves, a number of species populations, including among corals and mollusks, have decreased significantly.
