But there are two designated sites near the border, just outside the 12 nautical mile zone and managed by the Environmental Protection Authority (EPA).
Two companies hold permits to dispose of dredged materials - mostly sediment but also potentially containing a range of heavy metals - at these sites.
The permits require the companies to dump the material within 100 metres of the centre of designated dump sites.
But the EPA has revealed this condition was breached five times since 2016 – all by Coastal Resources Limited (CRL) (whose consent is now held by Marina Consultants Limited).
Their designated site, where it is allowed to dump 50,000 cubic metres annually, sits just outside the Marine Park border, 25km east of Aotea.
The majority of those breaches were outside the dump site by a few hundred metres, and generally due to operator error.
Three instances in 2016 dumped 348 cubic metres of material, and in January last year 680 cubic metres was dumped 283m from the intended location.
However, in February last year, 600 cubic metres was dumped 3.4 kilometres from the dump site closer towards Aotea, and inside the Marine Park boundary.
The EPA stated this practice was provided for under condition the consent, which states if material is disposed outside of the authorised area, it must notify the EPA and Auckland Harbourmaster within 24 hours.
CRL did notify the Director and Harbourmaster, stating that a technical issue had caused the barge to open outside of the authorised area.
The other site, an old navy dumping ground near Cuvier Island and about 20km from the Marine Park border, is where Ports of Auckland holds a consent to dispose of material dredged from the inner Waitematā Harbour.
The EPA said there had been no breaches at that site.
While legal, CRL's actions only reinforced the forum's position that marine dumping had no place in or near the Marine Park, MacDonald said.
The forum had unanimously backed reform to outlaw marine dumping, and this was a core part of their recent Briefing to the incoming Government, Macdonald said.
"We are calling on the Government to end this archaic practice," MacDonald said.
"We have a situation where 600,000 litres of pollution is going into our beautiful taonga, and it is allowed. Something is seriously wrong here."
They knew through various information requests the dredged materials often included high levels of mercury and heavy metals, MacDonald said.
"This practice has to stop."
The Herald has approached CRL multiple times for comment.
Minister for Oceans and Fisheries David Parker said he was aware of the Forum's concerns, but did not comment on whether he agreed with the call to ban the practice.
Dumping activities out to 12 nautical miles were the responsibility of regional councils under the Resource Management Act (RMA), while dumping that was managed by the EPA under the Exclusive Economic Zone and Continental Shelf (Environmental Effects Act) (EEZ Act).
"The RMA and the EEZ Acts both require a robust assessment of effects before any consents are granted, and consents routinely impose conditions to monitor dumping activities," Parker said.
"This reflects international best practice and our obligations under the London Protocol, which sets the framework for dumping of waste at sea."
Last year Coastal Resources Limited gained a permit from the EPA to increase its marine dumping to 250,000 cubic metres annually, but this was strongly opposed by mana whenua and many other Aotea residents.
Two island groups argued in the High Court the EPA failed to consult properly with local Māori and complained there was not a single public hearing on Aotea.
The High Court agreed, ordering the EPA to relook at the decision and listen to its own Māori Advisory Committee on who to consult.
On March 25 this year Coastal Resources Limited withdrew its application.
In their briefing, the forum also called for rapid action to address other the massive challenges facing the Hauraki Gulf.
The 2020 State of our Gulf report warned despite 20 years of advocacy, the legislation that set up the Marine Park had done little to address fisheries on the verge of collapse, sediment-choked and polluted waterways, and threatened biodiversity.
Among other goals, the forum was calling for 30 per cent of the Marine Park to be protected areas, and 1000 square kilometres of the seafloor to be replenished with shellfish beds.
