flippers

Flippers are broad, flattened limbs used for propulsion in water. The term applies to both natural biological structures in certain animals and to artificial devices worn by humans for swimming or diving.

In the animal kingdom, several lineages have flippers that enable efficient underwater movement. Cetaceans, including whales and dolphins, possess paired pectoral flippers and a large tail fluke that provides primary propulsion; the flippers aid in steering and braking. Pinnipeds such as seals, sea lions, and walruses have paddle-like forelimbs for propulsion, with hind limbs adapted for steering or mobility on land. Sea turtles have long forelimbs that function as flippers for forward motion, while penguins have wings evolved into rigid flippers used for underwater propulsion. Sirenians, including manatees and dugongs, have broad forelimbs that act as paddles. In each group, flippers reflect specific ecological needs and locomotion modes, ranging from graceful cruising to rapid underwater maneuvering.

Humans also use flippers in the form of swim fins or fins worn on the feet or hands to aid propulsion. Fins increase surface area, improving speed and efficiency in swimming, snorkeling, and scuba diving. Common designs include full-foot fins, which fit over the foot, and open-heel fins, worn with booties. Some divers use monofins, featuring a single blade for both feet, popular in freediving. Materials range from rubber and silicone to carbon fiber, with blade length and stiffness tailored to activity, skill level, and water conditions. Proper use emphasizes technique and safety to minimize joint strain and ensure control.