Swim (Str) Armor Penalty
Check: A successful Swim check allows a character to swim one-quarter his or her speed as a move action or half the character’s speed as a full-round action. Roll once per round. If the character fails, he or she makes no progress through the water. If the character fails by 5 or more, he or she goes underwater.
If the character is underwater (from failing a swim check or because the character is swimming underwater intentionally), the character must hold his or her breath. A character can hold his or her breath for a number of rounds equal to the character’s Constitution score, but only if the character does nothing but take move actions or free actions. If the character takes an attack action or a full-round action, the amount of breath the character has remaining is reduced by 1 round. (Effectively, a character in combat can hold his or her breath only half as long as normal.) After that period of time, the character must make a Constitution check (DC 10) every round to continue holding his or her breath. Each round, the DC of the check increases by 1. If the character fails the check, the character begins to drown.
The DC for the Swim check depends on the water:
Each hour that the character swims, make a Swim check against DC 20. If the character fails, he or she becomes fatigued. If the character fails a check while fatigued, the character becomes exhausted. If the character fails a check while exhausted, the character becomes unconscious. Unconscious characters go underwater and immediately begin to drown.