Hi not sure which islands you are referring too?, in the states waters you are boating in you should check with the parks sites to confirm where dogs are allowed, qld is a funny kettle of fish, some national parks do allow dogs on leash in specific areas and other areas they are prohibited, generally though all dogs apart from seeing eye dogs and assistance dogs are prohibited in national parks and ajacent marine parks inc beaches and intertidal flats.
Byfield nat park come to mind as dogs allowed in one particular spot on leash of course, and other places in nat parks are as you say not allowed above high tide mark on the beach Teewah beach on the great sandy nat park etc. This is because the beach is actually a highway of sorts.
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