THIS IS SUCH A GOOD QUESTION. Using real life examples, the ocean definitely has thousands/millions? or human corpses, and maybe some really big, Ancient lakes/Rivers, have ten-hundreds of dead bodies (maybe thousands? if they're really old) not that I've really thought about corpses in bodies of water before, but I feel comfortable after the fact, and would swim in oceans and lakes again, knowing there corpses.
Any body of water where I can see, smell or feel, or have seen smelt or felt a corpse, meaning any corpse I can distinguish as a corpse, to the horizon would be a body of water I could not swim in.
But in this circumstance, it's a pool, and I know of the corpse in the pool. The pool would be shallow, and the corpse, on the other end of a pool. I could probably swim in a pool, quite uncomfortably, as long as I couldn't see it when looking around all sides. It would also have to be really shallow, so I could stand up, assuming the corpse drifts over for a quick leaving protocal.