Looking for a fic I know I have saved, Rodney and John are on a jumper that crashes in the Atlantean ocean. They are separated by the door between the cockpit and back of the jumper and water fills the part where Rodney is but he doesn't drown and then he realizes he has a tail and gills. He eventually gets back to the area of the jumper John is in and convinces him to submerge himself in the water that is filling the compartment whereupon John changes too.
FOUND by ainamclane
FOUND by ainamclane