Hey Alex,
Its the small opening on the south side of the island that takes you towards the Keys opening and as you are headed toward the keys stay to the left of the light pole, if you go between the light pole and the right side of the bank headed in you will knock off your prop and or scag even if you are 100 yards from the bank. The north side of the island that is between 20 and the island is OK.
One more point, there is a light pole as you are coming in from the narrows towards Rattlesnake Island that is marking rocks, 30 yards past it toward the island there is another rock pile 1 foot above water that is not marked, this one will kill you if you are not careful also, I saw this one while I was fishing around that light pole, I almost ran up on it with my trolling motor.
What would it cost the county to put in a few markers? Not much, how much has it cost the public that drives from all over the US in broke scags and props or even worse, I would hate to guess
