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