The 18m, 60-tonne Sandra Kay, which sank at Careys Bay on October 10, spilled thousands of litres of oily water.
ORC harbourmaster Steve Rushbrook said there was no indication yet as to how the boat sank.
"The vessel has been righted but remains on the seabed," Mr Rushbrook said.
"The dive and salvage team are still working to refloat the vessel.
"Once refloated we will be better placed to ascertain the reason for sinking."
The ORC had recovered more than 3300 litres of mixed oil and diesel from the water and he was not aware of any environmental damage as a result of the spill, Mr Rushbrook said.
"We continue to monitor the pollution threat, and contain and recover as much pollution as possible," he said.
The next step was to refloat the vessel and work with the owner to make it safe, Mr Rushbrook said.
By yesterday afternoon, the vessel had been stabilised with buoyancy aids.
Asked about the cost of the operation, Mr Rushbrook said this was unknown as the operation was likely to continue "for a few more weeks yet".
The ORC may lodge for cost recovery against the owner of the boat, and ratepayers would not be "on the hook" for the costs.
Eldon Donaldson, of Careys Bay Marine Services, said his business had been assisting with keeping the oil spillage to a minimum.
The operation had gone very well, he said.
The boat has been linked to the recently paroled Charles Score Sanders, formerly of South Canterbury.
Mr Sanders was at Careys Bay following the sinking of a boat.
Mr Sanders — whose social media account features pictures of the vessel — was jailed for nearly four and a-half years in June 2021 for kidnapping, possessing a firearm and assault with a weapon.
