Septic tanks are causing serious problems.
With respect to city or county sewage the systems are often well past their use date, serve more people than they were designed for, and huge problems often go unrecognized for years.
Just south of Key Marathon is is a nightmare of a problem. On Little Torch there is a court battle going on and people are not maintaining their septic tanks while waiting for the outcome. All through the canals sewage is emptied as toilets are flushed and showers are taken. You can sit there and watch the sewage surface in the canals.
So many areas across the country, poor and wealthy, have serious sewage issues. Normally in the more wealthy areas the problem is dealt with like in the Keys. Most is taken out with the tide or settles at the bottom. It's less of a direct and immediate health issue. That's not to say it isn't generating environmental disasters along with serious health concerns. In more poor areas the problem is often a more immediate and direct health emergency.