Taranaki Regional Council is investigating whether one of the anchors used in the Waipipi Iron Sand operation has been removed from the South Taranaki seabed.
It was notified of the possible removal by Jeremy Penrice, an electrical engineer who has worked with subsea infrastructure in the oil and gas industry.
He lived in Patea as a child and remembers the huge ships anchored off Waverley from 1971-87 to be filled with iron sand pumped from an onshore mine.
Mr Penrice had talked to someone about the anchor system, and was later phoned by the person to say he had removed one of the anchors on January 9.
The removal was an illegal act by a "sophisticated Steptoe", Mr Penrice said, and he made a complaint to the council.