An environment group has raised concerns over new proposals for a marina at Coromandel Harbour, with fears that any dredging could cause harm.

The Thames Coromandel District Council (TCDC) recently sent a survey to Coromandel residents asking whether they would purchase a berth if a marina were constructed in the harbour.

The type, location and size of a potential marina have not yet been finalised, and the council has been working with potential marina developers to gauge whether there is any interest in one.

There are three different parties on a short-list with interest in building a marina and other ancillary facilities in and around the harbour.

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Thames-Coromandel Mayor Sandra Goudie said two of the proposals involve an unknown quantity of harbour dredging at this early stage, while the other included a boating marina on the end of a long pier, which will involve "a much lesser degree" of seabed disturbance.

A proposal to dredge a marina in Coromandel Harbour was declined 17 years ago because it failed numerous environmental tests in national legislation, including in the Resource Management Act and New Zealand Coastal Policy Statement.

Forest & Bird was concerned a new marina could cause damage to the coastal environment and release toxic metals that present a risk to human health.

"The new proposal doesn't define a specific site and size for a marina, but there is no point pursuing the same plans that a review committee rejected in 2000," said Forest & Bird's Central North Island regional manager Dr Rebecca Stirnemann.

"It's worrying that the TCDC is asking people to buy into the scheme when the public hasn't been advised about the environmental risks of constructing a marina that involves significant dredging.

"A marina proposal that requires dredging would impact on areas of mangrove, eelgrass and saltmarsh, and would cause an irreversible modification to the coastal zone."

Since the marina proposal was rejected in February 2000, the TCDC has commissioned two scientific reports, which both found significant levels of toxic heavy metals were present in the seabed of Coromandel Harbour, Stirnemann said.

"Since the last application, we have learned a lot more about the heavy metals in the Coromandel seabed, including mercury and arsenic."

"Dredging in the harbour would be dangerous for the marine environment and for people who eat fish and shellfish from the harbour, and would also threaten a booming aquaculture industry."

But Goudie said council staff and the Coromandel-Colville Community Board had developed a set of evaluation criteria for the proposals received and would continue to work with the various parties until a realistic concept has been determined.

Criteria include provision of docking for a ferry and charter boats, boat haul out, recreational boat ramp facilities, and ancillary activities.

Other considerations will include impact on the environment, operational sustainability and what degree of council funding and support could be required.

"There is a long way to go in this process including a full consideration of alternatives and a RMA process which we expect will involve full public notification and consultation," she said.

"To date we have received more than 160 expressions of interest in purchasing a marina berth, if a marina is to be built within the Coromandel Harbour, with over 80 per cent positive feedback from potential purchasers and the community."