An aquatic unit cannot leave underwater provinces without an item such as an Amulet of the Fish or Shambler Skin Armor which enables it to breathe air. If forced onto dry land by any means, it will suffocate and die.

Like Amphibious units, Aquatic units have -1 Encumbrance in their natural habitat, but will lose it if they go above water via items. This is not reflected in the recruitment screen.