People will walk through a forest that definitely has many corpses in it. Humans will not walk through an alley that has 1 corpse in it.

Humans have a corpse: proximity ratio that they find acceptable.

Edit: typo

It's less that there's a specific ratio of corpse:water but whether the corpses have been turned into fish poop yet.

You are a little soul carrying about a corpse.

–Some Roman guy paraphrasing some Greek guy.

I wonder if there is a point where the graphs of "perceived effect on the water" cross for both this experiment and homeopathy, and what that means.

Corpse size has a lot to do with it. I wouldn't swim in even a large pool with a dead human in it (knowingly), but one dead fish or rodent or dozens of dead tadpoles or bugs? Not an issue.

Heck, most household swimming pools have dozens of dead bodies in them, but they're 99% insects.

A lot of human survival is based on heuristics, if you can tell there's a corpse in something, you probably shouldn't drink or eat it... As a general rule of thumb

For large body of water since you're unaware of the corpse two kilometers away on the bottom, it's probably not an issue for you.

However, primal human heuristics are not calibrated correctly from modern media. There was the reservoir where somebody was caught on camera peeing into it, hundreds of millions of liters of water, and they decided to drain the entire thing to prevent the public concern. That's just a heuristic run amok