When any creature that isn't an aquatic goes underneath the water, they will begin to lose breath. Larger creatures have a longer amount of time before running out of breath than smaller ones. When the breath bar is exhausted, a player will lose 15% of their health every 1.5 seconds until dead. Returning to the surface of the water will refill the breath bar. Aquatic creatures have no breath bar and instead must manage their air supply.
Certain cave systems are designed deliberately such that certain areas are accessible to land animals only at low tide. Air pockets, rising water levels, and breath timers are balanced around the design of these areas such that it will kill players trying to pass at the wrong time in the tidal cycle.
Creatures possessing a grab can use it to their advantage to deliberately drown their opponents. Sometimes this is a safer way to kill one's prey than to attack them directly.
Talents that interact with the breath bar: