A creature with a lesser swim speed can move through water at its indicated speed without making Movement checks to swim, even during combat. It gains no bonuses to its Movement checks to swim, and must still make checks to navigate hazards or perform tricky tasks while distracted. However, while swimming, a creature with a lesser swim speed can make a Movement check to perform any actions normally possible with Acrobatics when on land, such as tumbling to avoid attacks of opportunity. Creatures without a lesser swim speed cannot use either Acrobatics or Movement in this fashion while swimming.
- Prone: Creatures with lesser swim cannot be made prone, but any time they are subject to the prone condition, they are instead slowed until the end of their next turn, after which it automatically clears (even if they don't move).
- Difficult Terrain: Creatures with lesser swim are not normally subject to ground-based difficult terrain, but they are subject to hazards like strong currents and vortexes which constitute difficult terrain in water.
- Permitted Movement: Creatures with lesser swim can perform charges and make 5-foot steps, but they cannot run or withdraw.