Did you know?
That we have a Foreshore And Seabed Endowment Revesting Act 1991?
The Act was passed by the then-National government in 1991, for the purpose of revesting in the Crown foreshore which was previously owned by harbour boards (there's a matching Dry Land Act which I haven't read). Interestingly, it includes a Treaty clause. However, it is the 1994 amendment which is of real interest - this set aside all Crown-owned foreshore and seabed and prevented the government from selling it except by specific Act of Parliament. (This is the status quo we all thought we had - a country where no-one could own the beaches, and where the government couldn't hock them off without anyone noticing)
But before anyone gets the wrong idea, there are two sticking points. First, as mentioned above, the Act applied only to foreshore and seabed already owned by the Crown; this was assumed to be everything that wasn't explicitly owned by anyone else, but the Maori Land Court may find otherwise in specific cases. Secondly, and more importanly, the amending Act specifically says it does not limit or affect "any interest in that land held by any person other than the Crown". National and ACT seem quite keen on ignoring this bit, but what it means is that if there was a Maori customary right over a patch of foreshore - or any other common law interest (such as a lease?) - it would not be extinguished.
DOC has a short bit on the Act and foreshore management here.