I don't thnk this has been posted yet. If it has I'm sorry, but i haven't seen it. Anyway in the borean tundra at the amber ledge there is a questline called "Monitoring the rift" where you monitor different magical disturbances. The second one requires you to go underwater and you get a buff that allows you to breathe under water! The neat thing is that it never expires. I camped out and came back and it was still there, I hearthed and jumped in the nearest body of water and it still worked. The only way to lose it is to die and then you can just get it back again