The ocean at Fort Myers Beach is very safe and very clean but you do need to be aware of possible dangers under foot. Stingrays are not always easy to see as they can bury themselves in the sand on the seabed. They don't take kindly to being stepped on and will sting if they are. The stings are not dangerous but are very painful.
Also, there can be various 'prickly things' on the sea bed, e.g. broken shells, so the advice is to shuffle your feet as you walk... thus alerting any lurking stingrays and making it less likely that you will step on something sharp.
"Shuffle your feet or you will do the stingray hop" tells the sign.
Fortunatly, only from May to October. The rays know the calendar and we had no problem with them because we were in Ft Myers in November 4th.