Monofin

A monofin is a type of swimfin typically used in underwater sports such as finswimming, free-diving and underwater orienteering. It consists of a single or linked surfaces attached to both of the diver's feet, emulating the fluke of Cetaceans like whales or porpoises. Even though the diver's appearance might be reminiscent of a mermaid or merman, monofin swimming is not the same as mermaiding.

The arrival of the monofin in the early 1970s led to the breaking of all finswimming world records by the end of the decade due to the improved performance possible when used instead of two ordinary swimfins.^[1]