You are accustomed to diving deeper than most would dare swim and can do so with less risk of drowning than even other experienced swimmers.
Benefit: You gain a +4 bonus on Acrobatics checks to reduce falling damage when diving into water and on Perception checks in dim light or darkness underwater. When attempting a Swim check to swim downward (at least 45 degrees down from the horizontal), on a successful check you can swim half your speed as a move action, or your speed as a full-round action. If you have a swim speed, it increases by 10 feet when you spend a move action to swim only downward.
In addition, you can hold your breath for a number of rounds equal to three times your Constitution score, and you gain a +4 bonus on Constitution checks to continue holding your breath after this time and to resist the effects of the cold environment underwater. Pressure damage you take from deep water is halved.
Pathfinder Roleplaying Game Ultimate Wilderness © 2017, Paizo Inc.; Authors: Alexander Augunas, John Bennett, Robert Brookes, John Compton, Dan Dillon, Steven T. Helt, Thurston Hillman, Eric Hindley, Mikko Kallio, Jason Keeley, Isabelle Lee, Jason Nelson, Stephen Radney-MacFarland, Alex Riggs, David N. Ross, David Schwartz, Mark Seifter, Jeffery Swank, and Linda Zayas-Palmer.