Auckland's aquatic backyard and prime fishing grounds are weed-deep in trouble from exotic caulerpa, a fast-spreading algae that smothers everything in its path.

There are calls for the government to spend hundreds of millions of dollars combating a fast spreading algae that looks to have a devastating impact in the waters of the Hauraki Gulf and beyond.

Opo Ngawaka is chair of the Ngāti Rehua Ngātiwai ki Aotea Trust.

Opo Ngawaka has lived on Aotea Great Barrier all his life, raising six children with his wife Elaine on the tiny island of Māhuki.

Living off the land and looking after nature are their way of life.

But that is under threat with the fast-spreading killer algae caulerpa.

"I've never seen anything like it," says Ngawaka, chair of the Ngāti Rehua Ngātiwai ki Aotea Trust.

The exotic seaweed which smothers anything in its way was recently found near Māhuki, off Aotea's west coast, a sign that it is spreading beyond the three harbours where it was first discovered two years ago, leading to a rāhui and ban on fishing with sinkers and anchoring.

This week, Aotea residents are meeting with representatives from Biosecurity NZ, an agency of the Ministry for Primary Industries, about how to combat caulerpa's spread. That includes discussion on an extension of the Contained Area Notices which enforce anchoring and fishing restrictions.

They're still hoping it can be eradicated but efforts so far have failed to stop new outbreaks and the thickening mats of the seaweed now cover up to 80 hectares in some areas.

Okupu Bay, on Aotea Great Barrier, post-Cyclone Gabrielle, covered in caulerpa.

Dr Barry Scott, a former science professor at Massey University and deputy chair of the Aotea Great Barrier Environmental Trust, says the lack of progress in tackling the pest is "staggering", not only on Aotea but in other areas at the top of the country including Northland, Hauraki Gulf, and Great Mercury Islands.

"It's sad, it's maddening, how Wellington has just not responded. There've been various iwi deputations to the former minister of biosecurity, they've banged on his table, they've written letters, there's all sorts of environmental groups around the Hauraki Gulf including ourselves who've written to the minister, and just nothing happens. A pitiful amount of money's been spent on it."

There have however been "endless meetings ... we're hui-ed out."

Scott has recorded a lengthy timeline of caulerpa since it was first discovered in Okupu at Aotea in June 2021, including media coverage and efforts by different groups and communities to persuade government ministers and MPI to act…

Go to this episode on rnz.co.nz for more details