I don't think you'll be stopped if you dress casually, but it is the most formal place in the area and most do dress to dine there.
See a wide range...when we were there, some folks were dressed up (suit, tie) others clearly in vacation garb (Polo, casual pants). I did dark jeans, button down, and blazer and felt like it was OK and not offensive to anyone. if you plan to sit at the bar, can definitely go casual.
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