Swim

You know how to swim and can do so even in stormy water.

Check

Make a Swim check once per round while you are in the water. Success means you may swim at up to half your speed (as a full-round action) or at a quarter of your speed (as a move action). If you fail by 4 or less, you make no progress. If you fail by 5 or more, you go underwater.

Water	Swim DC
Calm water	10
Rough water	15
Stormy water	20*

If you are underwater, either because you failed a Swim check or because you are swimming underwater intentionally, you must hold your breath. You can hold your breath for a number of rounds equal to twice your Constitution modifier (no longer then 1 round), but only if you do nothing other than take move actions or free actions. If you take a standard action or a full-round action (such as making an attack), the remainder of the duration for which you can hold your breath is reduced by 1 round. (Effectively, a character in combat can hold his breath only half as long as normal.) After that period of time, you must make a DC 10 Constitution check every round to continue holding your breath. Each round, the DC for that check increases by 2. If you fail the Constitution check, you begin to drown. The DC for the Swim check depends on the water, as given on the table below.

Each hour that you swim, you must make a DC 20 Swim check or take 1d6 points of nonlethal damage from fatigue.

Action

A successful Swim check allows you to swim a quarter of your speed as a move action or half your speed as a full-round action.

Special

• Swim Speed A creature with a swim speed can move through water at its indicated speed without making Swim checks. It gains a +8 racial bonus on any Swim check to perform a special action or avoid a hazard. The creature can always choose to take 10 on a Swim check, even if distracted or endangered when swimming. Such a creature can use the run action while swimming, provided that it swims in a straight line.
• Feats If you have the Athletic feat, you get a +2 bonus on Swim skill checks. If you have 10 or more ranks in Swim, the bonus increases to +4.
• Size The rules for familiars say "Small animals like these use Dexterity to modify Climb and Swim checks." Note however, that not all familiars are size Small. For example, bats are size Diminutive and cats are size Tiny. Therefore our guess is that the sentence, "Small animals like these..." isn't referring specifically to size "Small" but instead to creatures size Tiny or smaller (note though that not even all creatures size Tiny or smaller appear to have this applied to their skills.)