A proposal to mine the seabed off the west coast of the North Island is being defended by Trans-Tasman Resources.
About 300 people met in Raglan this weekend to oppose an application for a 20 year permit to mine iron ore from 65 square km of seabed, 22km off the coast of Patea.
Chief executive Tim Crossley said the company's research suggests the environment will recover in a matter of years.
He also said the mining will generate 250 jobs in New Zealand.
But the Kiwis Against Seabed Mining group said most of the work happens aboard ships. Chairperson Phil McCabe also said not enough is known about the effects of iron-sand mining.