The Oxygen Gauge appears as a timer under the Magic Meter, counting down until Link's remaining air supply runs out. Should the timer run out, Link will drown, unless he has a Fairy in a Bottle. However, if Link is wearing the Zora Tunic in Ocarina of Time or the Zora Mask in Majora's Mask, the Oxygen Gauge will not appear as he will never drown with this gear equipped.