A swim and skin-dive snorkel for providing positive end-expiratory pressure for pressure-balanced exhalation.The snorkel may include inhalation and exhalation conduits. Air can be exhaled into a chamber and released when exhalation pressure within the chamber exceeds a threshold pressure. The threshold pressure that must be overcome to achieve exhalation may be balanced against the compressive forces of the ambient water pressure acting against the user's chest and lungs, which may greatly reduce the resting expiratory flow rate, the minute respiratory rate, and therefore the overall work of breathing. The exhalation pressure may be linearly matched to the ambient water pressure as a function of dive depth, thereby discouraging exhalation while diving. A purge valve may also be placed at the lower aspect of the snorkel.