The council-owned company that owns the Opua marina is rejecting claims that it has damaged the seabed in the Bay of Islands.
Far North Holdings has won consent to extend the marina, but some Maori groups say the existing structure has already caused a big build-up of silt.
The company's chair, Ross Blackman, said seabed monitoring proves that is untrue.
However, Mr Blackman said there was a bad episode of siltation caused by dredging not long ago, when the regional council organised the clean-up of derelict oyster farms in the Waikare Inlet. As a result of that clean-up, sediment from the seabed ended up on the beaches.
Mr Blackman said would not happen when the company dredges to build the marina extension because the silt will be dumped behind a retaining wall.