Years ago, Key West built enough extra sewage treatment capacity to process sewage from the many cruise ships which visit the city. There was a plan to require all ships to discharge and pay for treatment so that sewage was not dumped 12 miles off-shore, which is only 3 miles past the reef. Captains get a bonus for fuel savings, so they tend to dump as soon as it is legal.
The cruise industry threatened to remove Key West from their list of stops, wrote some checks to the various non-profits, and the status quo was preserved.
The cruise ship industry is an ecological disaster, by choice.