The Y-40 Deep Joy is the worlds deepest pool. Y-40 is projected by Architect Emanuele Boaretto and supported by the “Boaretto Group Hotel and Resort”. The name Y-40 is inspired by mathematical symbols. “Y” is the ordinate axis of the Cartesian system and “–40” means the world's record depth or our pool- that is 40 meters underground. (Photo by Courtesy Y40 Deep Joy)

Filipino mermaid swimming teacher Genevieve Reyes (C) has her tail adjusted by students during a lesson by the Philippines Mermaid Swimming Academy in a private swimming pool in Makati, Manila, Philippines, 15 June 2013. The Philippine Mermaid Swimming Academy (PMSA) was created in 2012 in Boracay by Normeth Preglo of The Philippines and US swimming instructor Djuna Rocha. The swimming lessons were brought to Manila in April 2013. The price for a two-hour class is 37 US dollars. (Photo by Dennis M. Sabangan/EPA)

Girls prepare to take part in a mermaid lesson in Rio de Janeiro, Brazil May 28, 2017. Women in Brazil are not unique in their affinity for mermaiding. Classes are held as far away as Texas and some folks wonder if mermaiding will be the next fitness craze. (Photo by Pilar Olivares/Reuters)

Swimmers climb out of a pool carved into the thick ice covering the Songhua River during the Harbin Ice Swimming Competition in the northern city of Harbin, Heilongjiang province January 5, 2014. According to organisers, about 700 swimmers across China took part in the event on the official launch day of the Harbin Ice and Snow Sculpture Festival. (Photo by Kim Kyung-Hoon/Reuters)

A humpead wrasse, transported from Japan's southern island of Okinawa, swims with other tropical saltwater fish on display in a tank for the Sony Aquarium 2017 exhibition in Tokyo on July 31, 2017. The Sony Aquarium 2017 exhibition, featuring marine life common to the waters around Okinawa, runs until August 13. (Photo by Kazuhiro Nogi/AFP Photo)

In this undated handout photo taken by mrwed54, a woman poses for a photo by a lake in the Siberian city of Novosibirsk, about 2,800 kilometers (1,750 miles) east of Moscow, Russia. Thousands of Novosibirsk residents, from scantily clad women to newlyweds have been instagramming selfies near the lake nicknamed the “Siberian Malvides” after the far-flung tropical islands in the Indian Ocean. This is in fact is a man-made dumb of coal from a nearby power station that provides for most of Novosibirsk’s energy needs. Environmentalists are warning people against coming into contact with the water. (Photo by mrwed54 via AP Photo)

This picture taken on September 11, 2023 shows Moon Jellyfish (with rings) and Sting Jellyfish (yellow-orange inside) among a smack of a several thousand swimming off Seglvik, in northern Norway. (Photo by Olivier Morin/AFP Photo)

Grey seals show their playful side while swimming off the English coast, UK in the last decade of May 2025. (Photo by Brian Matthews/Solent News)