People swim underwater at Clovelly Beach on December 14, 2023 in Sydney, Australia. A severe heat wave hit Sydney over the weekend, a precursor of hot and dry conditions expected for the rest of the summer which will also bring heightened bushfire risk. The mercury rose to alarming levels again on Thursday. (Photo by Jenny Evans/Getty Images)

Matilda Thurston 10, enjoys a warm day at Hathersage Swimming Pool in Hathersage on April 27, 2025. A mini heatwave is set to hit parts of the UK with temperatures reaching 27 degrees next week. (Photo by Ioannis Alexopoulos/London News Pictures)

Zoi Karangelou of Greece compete in the Women's Solo Technical final on day one of World Aquatics Artistic Swimming World Cup Super Final 2025 at Xi'an Olympic Sports Centre on June 13, 2025 in Xi An, China. (Photo by Lintao Zhang/Getty Images)

Bottlenose dolphins swim over visitors in water tank at the Hakkeijima Sea Paradise aquarium-amusement park complex in Yokohama, southwest of Tokyo, Tuesday, July 21, 2015. Temperatures in Tokyo's metropolitan area neared around 96 degree Fahrenheit, or 35 degree Celsius, on Tuesday. (Photo by Shuji Kajiyama/AP Photo)

People dressed as mermaids and mermen take part in the group swim during the MerMagic Convention at the Freedom Aquatic & Fitness Center in Manassas, Virginia on March 4, 2023. The event bills itself as the “World's Largest Mermaid Convention”. (Photo by Joseph Prezioso/AFP Photo)

A caiman swims amidst trash in Canal das Taxas at the Recreio dos Bandeirantes neighborhood in west Rio de Janeiro, Brazil, on November 22, 2023. The urban expansion of the area and the resulting pollution have put the yacare caiman (Caiman latirostris) “in danger of extinction”. (Photo by Tercio Teixeira/AFP Photo)

Gold Medalist Kristof Milak of Hungary during the medals ceremony of the 200m Butterfly final on day five of the swimming competition of the Tokyo 2020 Olympic Games at Tokyo Aquatics Centre on July 28, 2021 in Tokyo, Japan. (Photo by Aleksandra Szmigiel/Reuters)

Ukrainians swim in an ice hole as part of the celebration of the Epiphany in Kiev, Ukraine, Monday, January 19, 2015. Orthodox believers celebrate the holiday of the Epiphany on Jan. 19, and traditionally bathe in holes cut through thick ice on rivers and ponds to cleanse themselves with water deemed holy for the day. (Photo by Sergei Chuzavkov/AP Photo)