Swim (Str; Armor Check Penalty)
Using this skill, a land-based creature can swim, dive, navigate underwater obstacles, and so on.
Check: Make a Swim check once per round while you are in the water. Success means you may swim at up to one-half your speed (as a full-round action) or at one-quarter your speed (as a move 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 rounds equal to your Constitution score, 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 or her 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 1. If you fail the Constitution check, you begin to drown (see Suffocation and Drowning). The DC for the Swim check depends on she water, as given on the table below.
| Water | Swim DC |
| Calm water | 10 |
| Rough water | 15 |
| Stormy water | 20¹ |
| ¹ You can't take 10 on a Swim check in stormy water, even if you aren't otherwise being threatened or distracted. | |
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 one-quarter of your speed as a move action or one-half your speed as a full-round action.
Special: Swim checks are subject to double the normal armor check penalty and encumbrance penalty (see pages 123 and 162, Player's Handbook). For instance, full plate incurs a -12 penalty on Swim checks instead of -6.
If you have the Athletic feat, you get a +2 boosts on Swim checks.
If you have the Endurance feat, you get a +4 bonus on Swim checks made to avoid taking nonlethal damage from fatigue.
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 always can 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.
Expanded Description - Complete Adventurer
You can swim more quickly than normal.
Accelerated Swimming: You try to swim more quickly than normal. By accepting a -10 penalty on your Swim check, you can swim at up to your speed as a full-round action (rather than half your speed or at half your speed as a move action (rather than one-quarter).
Expanded Description - Stormwrack
Naturally, the ability to swim and to swim well is a very useful skill for adventures in which you might go into the water at any moment.
Diving: Characters who dive into water take no damage on a successful DC 15 Swim check or DC 15 Tumble check, so long as the water is at least 10 feet deep for every 30 feet fallen. Water 30 feet deep is sufficient for a dive from any height. However, the DC of the check increases by 5 for every 50 feet of the dive. The table below summarizes these rules:
| Dive Height | Min. Safe Depth | DC | Damage for Failed Dive |
| 10 ft. | 10 ft. | 15 | None |
| 20 ft. | 10 ft, | 15 | None |
| 30 ft. | 10 ft, | 15 | 1d3 nonlethal |
| 40 ft. | 20 ft. | 15 | 2d3 nonlethal |
| 50 ft. | 20 ft. | 20 | 2d3 nonlethal + 1d6 |
| 60 ft. | 20 ft. | 20 | 2d3 nonlethal + 2d6 |
| 70 ft. | 30 ft. | 20 | 2d3 nonlethal + 3d6 |
| 80 ft. | 30 ft. | 20 | 2d3 nonlethal + 4d6 |
| 90 ft. | 30 ft. | 20 | 2d3 nonlethal + 5d6 |
| 100 ft. | 30 ft. | 20 | 2d3 nonlethal + 6d6 |
| 110 ft. | 30 ft. | 25 | 2d3 nonlethal + 7d6 |
| 120 ft. | 30 ft. | 25 | 2d3 nonlethal + 8d6 |
| 160 ft. | 30 ft. | 30 | 2d3 nonlethal + 12d6 |
| 210 ft. | 30 ft. | 35 | 2d3 nonlethal + 17d6 |
| 240 ft. | 30 ft. | 35 | 2d3 nonlethal + 20d6¹ |
| ¹ Maximum falling damage. | |||
If the water is not deep enough for a safe dive, add 5 to the DC and treat your dive or fall as 30 feet higher than its actual height on the table above.
Extra Breath: As a move action, you can prepare yourself for a long submergence with some careful breathing. On a successful DC 15 Swim check, you can add 4 to the number of rounds you could otherwise hold your breath, provided you start to hold your breath immediately after making the check.
Swim Speeds And Heavy Loads
Much as flying creatures can't fly while carrying a medium or heavy load, creatures who are natural swimmers can't use their swim speed while carrying a heavy load. (Heavy armor does not necessarily constitute a heavy load.) A swimming creature that can't use its swim speed can still swim, in the sense that it can make progress through the water - but it has to make Swim checks just like a creature without a natural swim speed (although it still gets its racial bonus for having a Swim speed), and its speed is reduced by half.