The quickest way to find out if it's legal to land on a stretch of water is to go and land there. If no-one says anything you're laughing, and if someone does say anything they'll probably tell you which law you've broken and from there you can reverse engineer the procedure for getting the permission.
(Although I conceed that it might prove expensive and you might not get to do it again.........
)
On the positive side, you would be well qualified to come back here and tell us the correct procedure!
Small print: I do so hate to conceed that in today's litigious world it is now necessary to add a disclaimer in that none of the above is meant to be taken as legal advice and anyone confused or misguided enough to construe it as such should seek urgent medical attention.
I also realise at this point that the smallest font size on here is not sufficiently small to make my small print look anything like real small print but if I continue adding text then the paragraph(s) may indeed begin to resemble something that might, to the casual observer, be akin to genuine small print rather than the inane ramblings of someone who's bored and tired and should really be tucked up in bed at this hour ready for another busy day at work tomorrow.