Legally, you have to be already IN the water to empty your bladder or your bowels into the water. Anything else is illegal.
Last summer at a raftup, a certain acquaintence who shall remain nameless, spent the whole day in the water up to his armpits, drinking beer all day long. He was completely legal.
But, if he were out of the water and used the swim platform to take a whiz, he'd be in violation of the law. (Of course he wouldn't do that, as there were about a dozen other people present at the time).