Swim Skill

Check
Make a Swim check once per turn while you are in the water. Success means you may swim at one-quarter of your speed (as a movement action). If you fail by 4 or less, you make no progress through the water. If you fail by 5 or more, you go underwater.

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 turns equal to your Constitution score, but only if you do nothing other than take movement actions. If you take an action phase, the remainder of the duration for which you can hold your breath is reduced by 1 turn. (Effectively, a character in combat can hold his or her breath only half as long as normal) After that period of time, you are inflicted with drown.

The DC for the Swim check depends on the water, as given on the table below.

You can’t take 10 on a Swim check in stormy water, even if you aren’t otherwise being threatened or distracted.

Epic Check
You can swim up vertical surfaces, or swim much faster than normal.

Swim up Waterfall
This use of the skill allows you to swim an angled or vertical surface, as long as you remain completely or mostly immersed in water. Other examples might include swimming up a whirlpool or an incredibly large wave.

Speed Swimming
By taking a –20 penalty on the check, you can swim your speed as a move-equivalent action.

Action
A successful Swim check allows you to swim one-quarter of your speed as a movement action.

Special
Swim checks are subject to double the normal armor check penalty and encumbrance penalty.

A unit 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 unit always can choose to take 10 on a Swim check, even if distracted or endangered when swimming. Such a unit can use the run action while swimming, provided that it swims in a straight line.