Aqua Wank
The action of masturbating within a body of water, excluding the bath tup, e.g. a wank in the ocean, (or more extreme a swimming pool.)

It can also be made wank into a game, the more fish around your semen, the more successful the wank. compare with your friends and others of a similar disgusting nature, and see who is the best at 'beating off the fishes'.
holy shit, should of seen my aqua wank trail, I had a school of fish following me! beat that!