One presumes, since it had long been established that Dorma can't breathe out of water at all, that this is IN water. You certainly can't tell it, though. No concession to it at all--no plants swaying, no bubbles, no guppies swimming by... zip. Isn't that some sort of smoke rising from whatever that is on the right? Perhaps they just forgot he was supposed to be under the sea.
The book was still well-written by "Roy the Boy" but seemed to be coasting a bit at this time.