Definitely not an American expression, Fee! And as I've certainly revealed, I'm not up on my NZ slang.

Actually, there are some laws against the public participating in clean up. The water was contaminated by sewage, fuel, chemicals, and anything else from buildings that got flooded, so the debris and mud itself are potentially dangerous. And there are some items that might be dangerous in themselves: industrial waste, medical waste, etc. The authorities have been strict about waiting for licensed contractors to do most of the work. And so we wait.

There are certainly things that community members can do, and many are doing a lot. But clean up isn't generally among them.