Snuba (a portmanteau of "snorkel" and "scuba") is a method of underwater swimming in which the swimmer uses the swimfins, diving mask, weights, and breathing apparatus commonly used in scuba diving, but the air tanks which are usually strapped to the back are instead laid horizontally in 5'-long rubber pontoon rafts that remain on the water's surface. Snuba is typically used as a form of "introductory diving" (diving done in the presence of a professional, insured guide, and following a very short lesson, but not requiring a SCUBA certification).