The Okura Environmental Group says plans to develop 130 hectares of coastal land north of Auckland will have disastrous effects on the nearby marine reserve.
Chairman Peter Townend says an access road built by Todd Property on the land near Okura Estuary has resulted in high levels of sediment.
"This is the last bit of coastal land available ... there's no more ... it's gone so ... excuse me getting upset about it.. but it's just ridiculous," he said.
Last week, the Auckland Unitary Plan Independent Hearings Panel recommended moving the rural/urban boundary, allowing Todd Property to proceed with plans for 750 houses on the site.
Auckland Council opposed the proposal, saying contaminants from urbanisation were likely to have an adverse effect on the estuary.
Okura Estuary is home to a number of species including dotterels and variable oyster catchers.
Todd Property says it is helping to ease the Auckland housing crisis, and that there will be no environmental impact.
"Our proposal is focused on responsible and sustainable development - building much-needed homes for families while protecting the marine environment," it said in a statement.
The company has also pledged to put aside 40 per cent of the development for parks and walkways.
The council will make its decision on whether the proposed development goes ahead in three weeks' time.