Take caution to some certain aquatic creatures that can harm swimmers or divers in the ocean. Here are the facts obtained via NEFSC Fish FAQ:
"The barracuda (though divers claim its ferocious reputation is undeserved), moray eels, octopuses, and sharp-spined sea urchins can be dangerous to swimmers. The Portuguese man-of-war has tentacles up to 50 feet long with specialized cells that produce painful stings and welts on contact by swimmers."
"Sting rays, toadfish, catfish, and jellyfish can inflict damage on swimmers and waders. Certain coral-reef organisms are to be avoided by divers."
For more info about those respectative sea creatures including preventative measures, visit Aloha.com
For example - " Prevention of Sting-ray attack: Shuffle feet when walking in shallow inshore waters. Stay clear of disturbed (swimming) ray. Do Not Molest!"
"Injury mechanism - Tail with poisonous barb near base of body."
Sometimes accident happens while swimming in the oceans. Be aware of this preventative measures. It might help save your own/ppl's lives. Peace.