Expert Swimmer( Stormwrack, p. 92)
You swim like a fish. You can stay underwater far longer than others of your race, and you are at home in the water.
Endurance (PH) , Swim 4 ranks,
You can hold your breath for 3 rounds per point of Constitution. You gain a +4 bonus on Constitution checks made to continue holding your breath. On a successful Swim check, you swim your land speed (as a full-round action) or half your land speed (as a move action). Your natural swim speed increases by 10 feet, if you have a swim speed.
You can hold your breath for a number of rounds equal to twice your Constitution before you are at risk of drowning. On a successful Swim check, you swim half your land speed as a full-round action, or one-quarter your land speed as a move action.