This rule applies to any water near land. You get runoff from dog, cat, bird defecation among whatever chemicals may be found on land. This is even if storm water sewage does not overflow.

I lived in Key West for half of my life. I got addicted to swimming daily and would always go, no matter what. Now I have sinusitis caused cluster headaches. When I trace back events, the first one happened about a year into the swimming. Now they are truly debilitating.

I would even add not swimming during an out-going tide if the water passes by nasty land. (nasty = like seemingly lovely mangroves where birds live or bird poo covered rocks)

Now I always check water quality reports to find the cleanest water on vacation as well. Most places do them, even if not advertised.