Is there some practical reason preventing spells such as water walking and
racial abilities such a flight from modifying the endurance cost of moving
over water, either with a flat reduction or in a manner such as hiking? It
seems to me that any square requiring a swim skill check should not drain much
endurance if the character doesnt need to swim or is magically able to do so
more easily. It might be a nice uptune for aquatic races now that trees are
gone. Should be easy to tie the check into the cost anyway.