sundevil,
scuba diving, like every activity, is regulated differently in every jurisdiction. As is access to all resources,
marine or shore. At last count there were 192 nations in the UN and perhaps a few not in it, so there will be at least 192 answers to your question.
Last time I heard, in some places where there has been a lot of archaeological pillage with
SCUBA gear, like
Egypt and
Greece, if you put on a tank and go in the
water without permission, you can expect be to arrested for the simple crime of using the
equipment. I haven't bothered researching that to find out if it is true.