Kiwi's tick differently

But the cops can't actually get out there to stop them. And it's just local law.

It's still illegal. The whole point of this charade is to avoid breaking the law. If they wanted to drink illegally and not get caught they'd just do it at home.

Local law is basically valid until where ever the cops don't feel like going. I highly doubt the cops want to go through the process of getting a boat to actually go out and fine them. The reason the don't want to do it at home is because it's easy/boring/not actually illegal. The ban was only a public one.

In most places in New Zealand during the New Years period, they have set limits for where alcohol can be consumed. For example, Queenstown, which had the entire town center, the Queenstown Gardens, and the waterfront. These zones were shaded in red. What was not covered was the lake itself, meaning alcohol consumption is fair game. Assuming this town functions in the same way (a fair assumption given the similarity of most district councils), this is perfectly legal.