An Amphibious unit may enter underwater provinces without penalty.
Poor Amphibians may also enter, but will receive penalties to their attributes: -3 attack and defense skill, +1 Encumbrance, Combat Speed halved. Some units, notably Turtle Warriors and other Mermen, will be marked as poor amphibians in their land shape but transform into full amphibians when moving underwater.
Both types can swim over rivers.
See also: Aquatic.