First: there is no statute prohibiting nakedness in public. In cases of ‘public nakedness’ the police go to the Summary Offences Act 1981 and consider:-

• S27 Obscene/Indecent exposure
Obscenity requires some element of lewdness or lasciviousness, so this charge is regarded as inappropriate for a case of mere nakedness.

• S4 Offensive behaviour
The Ceramalus case of 91 (an appeal to the High Court won) determined that the legal definition of 'offensive' was not met by mere nakedness (even in the presence of school children), in a place where nudity was 'not uncommon' or 'known to occur'.

• S4 Disorderly behaviour
The Ceramalus case of 95 (appeal to the High Court lost, appeal to the Court of Appeal declined) indicates that 'the street' is not a place where nakedness is known to occur.
So that's why it cannot always be specified that you can or can't go naked (ie: be forensically ‘disorderly’).
In your own backyard, for instance, if a neighbour decides to take offence and call the police, they may well 'act.' In general though, District Court judges in these cases tend to follow
'expectation', tested with the evidential reaction of those around.
Having said that though, there is a forceful argument worthy of note! In 1990 New Zealand enacted a statute to affirm recognition of the International Covenant on Civil and
Political Rights, and the Universal Declaration of Human Rights; which both declare the human person to have inherent dignity and worth. That statute is the Bill of Rights Act. That ‘dignity and worth’ obviously must apply to the complete human person – if it is not the whole person, it is meaningless. Therefore no part of the being which has inherent dignity and worth, can be rationally determined to be an attack on society. No mere part of a human form can rationally ‘offend’ or ‘disorder’ the average reasonable person – as conflated with the Bill of Rights. If that average reasonable person, that is: the Bill of Rights Act; is not offended or disordered, a reaction that is inconsistent with that now defined norm, must be forensically unreasonable and thus disregarded.

In the case of a local body/Authority,
As with the example of the North Shore City Council and
St Leonard's Bay, any bylaw can be enacted, but it cannot impose a penalty greater than that of statute. Since there is no statue law forbidding nudity, no penalty should apply. However, since the present situation is that current ‘case law’ rules, the fact that mere nakedness is legal ‘in a place where it is known to occur’ or ‘is not uncommon’ also means that no penalty can apply – as there is plenty of evidence that nudity is ‘known to occur’ at say St Leonard's Bay.