good question.. honestly I don't know.. however get in good with a 13th level summoner or a druid, I know both of those classes get spells that allow them to breathe underwater.. the summoner one creates an item which will last for about 30 min or so... can't speak for the druid one since I don't have a druid, I've only seen it used by a druid friend.
I belive the Totem of the Otter has the effect of Endurance Breath. Be warned these have short durations (3 mintues) and are not stackable.. But can be crafted in volume.
There is a quest that starts at the NPC that gives a quest behind the first shack on the left walking onto the docks in Thundering Steppes. I think you have to be level 25 to start it.
It is a Heritage Quest for the Fishbone Earring, which gives you Enduring Breath. Seems the quest giver is a decendant of Hadden. =p
Clerics have the spell 'Enduring Breath' which allows the recipient to breathe underwater for at least 15 mins with the App I spell. I would look for one of them first if it's just going to be a quick thing to get somewhere/something...