Local iwi, hapū and community members will declare Maitai Bay and neighbouring Waikato Bay on the Karikari Pensuila a no-take zone from next Wednesday, December 20.
It will last for more than two years until March 2020.
Rāhui coordinator Whetu Rutene says the marine environment resembles a wasteland.
"Kina barrens have just completely taken over. There is no seaweed, there is no fish life, and it's slowly creeping further out," he says.
The explosion in the number of kina, or sea urchins, is being put down to overfishing.
"Their predators are crayfish, large crayfish, and snapper primarily and we've reduced those big animals on the reef to almost nothing," says marine biologist Vince Kerr.
The decision to impose a rāhui comes after extensive hui and consultation.
"Whether they have a bach in our community or whether they live there or if they're part of the iwi, whānau, hapū, we've reached out as much as we could," says Mr Rutene.
"We haven't had much resistance - if anything, we haven't had any resistance at all. The whole community agrees that there is an issue around the sustainability of our rohe."
Mr Rutene says the local iwi, Ngāti Kahu, and the two hapū in the area - Te Whānau Moana and Te Rorohuri - have agreed to suspend fishing and diving in the area.
"When we use a customary tool like a rāhui, that means everybody has to adhere to what we're trying to achieve," he says.
"That means an absolute no-take from absolutely everybody."
The Ministry for Primary Industries is the only organisation that could legally enforce the rāhui.
Spokesperson Steve Rudsdale says while they back the initiative, the bay is in no more danger than other areas in Northland.
Mr Rutene says the response by authorities, so far, has been disappointing.
"It has been a little frustrating that relevant organisations have refused to endorse what we're doing. We expected and had hoped for better."
Northland Regional Councillor for Te Hiku Mike Finlayson believes the rāhui is "fantastic and should be endorsed".
"It's a very iconic spot," he says. "It needs protection and a rāhui is a great way to do it."
Mr Finlayson says he's raised the issue with NRC, but says it hasn't gone very far.
However, he takes heart from a High Court ruling in Tauranga that regional councils may have the right to legislate in the marine area out to 12 nautical miles.
"If the biodiversity is being threatened that would imply we have the right to regulate in there, but the rāhui is a different tool and perhaps we should watch and see how it works."
A team of marine scientists from the Mountains to Sea Conservation Trust are also supporting the rāhui.
Vince Kerr says they have put aside a small budget to set up a monitoring programme, which will help track the recovery of marine life.
Department of Conservation spokesperson Abigail Monteith says, while it can't police the rāhui, it will give out pamphlets and put up signs at the nearby DOC-run campground.
A ceremony to impose the rāhui will take place next Wednesday morning from 5am at Maitai Pā, with the community and local authorities invited to attend.