Ordinary swimming outside the combat-control rules below follows normal d20 Swim rules. Swim checks use the Athletics skill.
When a creature takes damage while swimming, it must attempt an Athletics (Swim) check before its next attack while swimming to maintain control. The DC is 10 + the net HP damage from that hit after damage reduction, following the mounted-combat damage stability formula. If the swimmer takes damage multiple times before that attack, it makes a separate check for each damage instance. On a failed check, the swimmer loses control and begins sinking.
A creature that loses control while swimming sinks 30 feet during the first round and 60 feet during each subsequent round.
A creature that is sinking can use a Move Action to attempt an Athletics (Swim) check to regain control. The DC is 10 in calm water, modified by environmental conditions; it does not increase with distance sunk. On a success, the creature stops sinking and regains control of its swimming. On a failure, it continues sinking and can try again with another Move Action.
| Environmental condition | Athletics (Swim) DC modifier |
|---|---|
| Light current | +2 |
| Strong current | +5 |
| Light storm | +5 |
| Heavy storm | +10 |
Apply all relevant environmental modifiers cumulatively.