I dont recall pooping in the water in Baja but I did in fact once do this in the Baltic sea.
I was on an island that is half Germany and half Poland... right on the border... snorkeling around in the Baltic Sea. There was people around but nobody near me. I felt a sudden urge that I had to go, and BAD. I love euro food but sometimes my stomach can't handle it that well. The nearest public toilet was over a block away from the beach and I knew I wouldn't make it. So I went stealth mode, pulled my pants down in the water and let 'er rip while I swam, making sure nobody could see me pooping. It was pretty nasty, it was a bunch of chunks floating in the water. There are no waves like here in California so it was just floating around.
As soon as I finished, I started making my exit to the beach, when I noticed a young guy and a girl (couple) frolicking in the water, splashing eachother and just having a good time. They were headed in the direction of the disaster area.
By now, I was already 100+ feet away, on the shore, watching the couple from afar. They were in ground zero. The girl seems to have spotted something in the water! What could it be? I felt dirty just watching the events unfold. I thought "is this really happening".... The girl picks something up in her hand and inspects. She doesn't know what the waterlogged, soft brown chunk is. Is it mud? She brings it closer to her face. Suddenly, in a seisure-like action, she throws her new treasure a few feet away and with a disgusted look on her face, starts yelling something to her boyfriend.
I was silently laughing to myself on the beach, but in retrospect i think it was pretty damn nasty. Little did they know, the culprit was watching them from afar like some sort of sick weirdo. I didn't do it on purpose!!