A method of treating a fluid stream underwater comprising integrally attaching a skid to a fluid stream treating vessel so that the fluid stream treating vessel can be disposed on an underwater floor in a position such that an opening in said vessel is at a highest point on said vessel when disposed on the underwater floor; remotely directing a fluid stream treating vessel to an underwater floor location sufficiently close to said fluid stream so that the fluid stream can be remotely attached in fluid communication with said fluid stream treating vessel; remotely connecting said underwater fluid stream to said fluid stream treating vessel for treatment of said fluid stream; treating said fluid stream by contact with a treatment media disposed within said treatment vessel, maintained at equilibrium water pressure at the depth of treatment; and flowing the treated fluid stream out of said treating vessel.