There are plentiful stonefish (potentially lethal sting) near Playa Ejertivo - be extremely careful of wading in the rocky areas.

There are occasional coneshells (also potentially lethal) scattered about. 

Giant stingrays (awesome!) live in the deeper waters off Playa Larga - swim a little further out toward the end of the buoy-marked swim area.

The water is not safe to drink here - hotels don't necessarily clue you in by offering or providing bottled water

Little to do on this island, bring a book as no stores on the island have any to sell you.

Book a year in advance around Christmas. You can just show up though, in July.