The company running the Marsden Point Oil refinery says it understands locals' concerns at its plans to dredge Whangarei Harbour.
It wants a deeper, straighter channel to take bigger ships, moving 3.7 million cubic metres of sand.
However, Patuharakeke trustee Juliane Chetham says they're worried about the impact on shellfish and marine mammals.
"The majority of tangata whenua think the harbour is already in a degraded state, and we are quite concerned of the cumulative effect of this proposal on top of the industrial projects that have already happened," she told Newshub.
"Given the state of the pipi and mussel beds, we're quite worried. We'd prefer the harbour was left alone."
Refining NZ chief executive Sjoerd Post saying they're willing to listen to local Māori and community groups.
"There are a large number of concerns - what is the impact on whales, what is the impact on orcas, what will happen to the sandbanks - and that's why we have spent a considerable amount of money getting consultants in to tell us well, if you dredge the harbour, these are all the consequences."
The first public information days about the proposal are being held this Saturday and Sunday outside the Claphams Clock Museum in the Whangarei Town Basin.
Refining NZ says dredging the Whangarei Harbour is vital to ensuring the refinery stays competitive. Currently ships can only enter the harbour under loaded, which isn't cost effective.
"The refinery in Whangarei is in competition with refineries in Korea and Singapore. Our customers have a choice - they already import 30 percent of their products, and they could easily one day tell us, 'Look mate, we're going to import all of our products."
"The experts actually think on balance, bringing these ships in fully laden - and therefore fewer ships - is actually safer than what we do today, so that could actually be a really positive outcome of what we propose."
Ms Chetham says any benefits will only be short-term.
"The question we are pondering is whether that outweighs any potential negative effects on the harbour in Bream Bay."
Northland MP Winston Peters says it's a "no-brainer" to go ahead with the dredging.
"It's seriously important for jobs, and for the wider community it's pretty essential. We can't afford to pass up opportunities like this."
Mr Peters says the port is presently under-utilised.
"This is a utility that we cannot up here, nor the country, afford not to develop… it's one of the greatest assets, undeveloped, that Northland has, that New Zealand has."