Underwater. Note: not to be confused with Equestrian, for those of us who assume otherwise. It does involve the water but does not, in any way shape or form, involve horses
Person 1: Dude, where are you?
Person 2: I am aquestrian. If you go aquestrian you will see me.
One who travels by water. Using the same reasoning that a person who travels by horse is an equestrian and a person who travels by foot is a pedestrian then a person who travels by water is an aquestrian. I coined the word for my own use when I first named my sailboat in 1987. I am not aware of any documented use of the word prior to that date.
He travels in a world of constant motion and is an aquestrian.