The vile act of crapping while in the ocean. Occasionally committed by those surfers who are too lazy and/or unmotivated to get out of the water to deuce like a normal person. In fact, some surfers deliberately do it to "mark their terrirory", or do it to mark the end their surf session, leaving it behind it as an "I was here" statement.
-"Saturday was nothing but music, beer, surfing & aqua turding." *lmao*
-"You'd want to avoid that spot in the water, that's where Ronny went aqua turding....and unfortunately he had a bout of diarrhea." *lmao*