Not even
I (the king of "help yourself") could figure out a legal way out of this one. Someone building a beach . Trapping sand with jetties ? digging out their own lagoon inland from the "normal" beach?, etc.... So they don't qualify for the "public" (high to low tide) national navigable water laws. If I'm understanding the Hawaiian posters here (and what they were told by the security as the evolution).
And you think you could fight that ? To tell them it's not private since "salt water touches it" ?
Ok, I'll get the popcorn ready. A bunch of us will pitch in for an airline ticket, and fly you out there. Go at high noon and bump into the same fellow as the OP did. I'd love to see the latest installment of the scuba adventures on this !