A swimmer stops short of a red algae bloom at Sydney's Clovelly Beach on November 27, 2012, which closed some beaches for swimming including Bondi Beach for a period of time. While the red algae, known as Noctiluca scintillans or sea sparkle, has no toxic effects, people are still advised to avoid swimming in areas with discoloured water because the algae, which can be high in ammonia, can cause skin irritation. (Photo by William West/AFP Photo)

Members of the Coney Island Polar Bear Club warm up before swimming at the beach at Coney Island in New York, December 15, 2013. (Photo by Eric Thayer/Reuters)

A squid swims underwater off the shore of the coastal city of Qalamun, north of the Lebanese capital Beirut, on September 24, 2019. (Photo by Ibrahim Chalhoub/AFP Photo)

A wild water monitor (Varanus salvator) is seen swimming between colorful popcorn snacks at a Lumphini public park in Bangkok, Thailand on March 27, 2022. (Photo by Matt Hunt/Neato/Rex Features/Shutterstock)

Lucy Blacker from Australia takes to the water at the 40 Foot for a Christmas Day Swim in Ireland on December 25, 2022. (Photo by Alan Betson/The Irish Times)

Team China performs during the team free routine artistic swimming competition at the 19th Asian Games in Hangzhou, China, Sunday, October 8, 2023. (Photo by Aaron Favila/AP Photo)

A puffin swims underwater in search for fish off the coast of the Farne Islands in Northumberland, North East England in the last decade of July 2025. (Photo by Brian Matthews/Solent News & Photo Agency)

A man walks past kelp as he goes for a swim in the Pacific Ocean at La Jolla Shores, Thursday, July 24, 2025, in San Diego. (Photo by Gregory Bull/AP Photo)