I am used to seeing icky contaminated run off like this. From here. UPDATE: I think this is bubbling up from landfill (we have over 200 different sites around Auckland City). I have asked Auckland Council about it.
But this is just weird, it dries hard. Like the mud is covered in milky ice. I found it here.
I didn’t really get how zinc from galvanised roofs could be poisoning the estuary until I made this map. I found a presentation by Marcus Cameron which suggests that sites the source (the head of the estuary) are trending up (more zinc). At the same stormwater conference Judy Anne Ansen showed a pie chart on Industrial (Mt Wellington) zinc sources with about 80% attributed to roofs.
Marine report card for Tamaki is here: