To use a snorkel.
A snorkel parka.
A retractable tube fitted in diesel-engine submarines to allow sufficient ventilation that the engines may be used at periscope depth.
A hollow tube, held in the mouth, or mounted on and opening into a diving mask, used by swimmers for breathing underwater.
To remain afloat in the water without use of any buoyancy aid, by using kicking motions and hand motions.
To make no progress, expending effort just enough to maintain a stable position.