Eleven thousand tonnes of steel from the wreck of the Rena sits on Astrolabe Reef, five-and-a-half years after the container ship struck it.
Captain Roger King was giving evidence to an Environment Court appeal hearing in Tauranga today.
The marine consultant was called by Astrolabe Community Trust which obtained consent to abandon the remains of the Rena. It sparked seven appeals of which two remain following mediation last May.
Mr King said the wreck had transformed from having a major impact on the reef to its current state where the reef had integrated the wreck as part of its environment.
"That there is a significant amount of shipwrecked steel at the site is indisputable. However, I have observed the remaining steel structures become colonised with coralline, soft corals and kelp. In some cases, it has become indistinguishable from the adjacent reef structure."
Mr King, who has dived 40 times on the wreck, said he had seen marine life progressively return to abundance in the area formerly comprising the debris field.
Seven to 12 tonnes of copper had dissipated or remained trapped in the collapsed remains of the Rena while at least nine tonnes had been recovered.
TMC Marine Consultants estimated that less than one cubic metre of oil remained within the wreck, at depths and in locations where it was no longer safe or feasible for recovery by divers.
TMC technical director Colin Barker said it would take up to three years and cost between $388m and $560m to remove the aft section of the wreck.
He said there was general agreement among experts that the parts of the aft section in deeper water were beyond safe or feasible air diving depth. The alternative of saturation diving was unlikely because of strict guidelines.
Mr Barker said the removal of the 1000-tonne bow lying in shallow water remained problematic because it was beyond the reach of moderately sized off-shore cranes. It would have to be manually cut out by divers and dragged into deeper water, with the total operation lasting about 410 working days and costing $89m.
The shallower bow section was heavily affected by current and swells that precluded dive operations in all but the calmest weather.
He said the 111-day weather downtime of Resolve Salvage's $43m 244-day operation removing debris from the debris field showed the magnitude of the time and costs involved in operations at Astrolabe Reef.