The New Zealand navy ship ran aground, caught fire and sank off the south coast of Upolu in Samoa earlier this month.
HMNZS Manawanui - a specialist dive and hydrographic vessel - had been conducting a reef survey when it hit the reef.
The island nation's Marine Pollution Advisory Committee said there was substantial damage to the reef from the Manawanui's collision and friction from its anchor.
The Manawanui was lying about 35 metres below the water off the coast of Tafitoala, according to the committee's latest report on the sinking and its aftermath.
Committee chairperson Fui Tupai Mau Simanu told RNZ divers were at the site to gather more information and to stop the fuel leaking.
Ultimately, the plan was to remove the remaining fuel from the Manawanui, he said.
Chief of Navy, rear admiral Garin Golding, told Morning Report some 950 tonnes of diesel fuel were on board the Manawanui when it sank. The fuel is a lighter oil which can partially evaporate, leaving long-chain hydrocarbons that are relatively less toxic.
Sources had suggested to RNZ concerns had been raised about potential oil leakage from the ship's engine before it left.
Golding was asked to provide assurance the ship was fully operational, with no concerns about maintenance prior to leaving.
"The ship was in a maintenance period," he said. "It conducted that, they did trials post that maintenance period, and the ship was determined safe to deploy for their operation."
RNZ Pacific reporter Susana Leiataua is in Samoa and said the damage spanned 5000 square metres, but there was no sign of oil contamination on the reef and coastline.
RNZ is expected to speak with Commodore Andrew Brown, the Defence Force's Deputy Chief of Navy, in Samoa later on Saturday.
