The New Zealand shipping authorities admitted Thursday that a \"reasonably significant amount\" of oil remains on a ground cargo ship and it is still leaking more than two months after the accident. Maritime New Zealand (MNZ) officials said the operation to remove cargo containers from the Liberian-flagged Rena had made no progress since Nov. 29 because of bad weather, which was also causing more heavy fuel oil to leak and wash ashore. MNZ salvage unit manager Arthur Jobard said in a statement that salvors had installed patches in the corridors of the wreck to enhance buoyancy of the vessel, which ran aground on the Astrolabe Reef, about 12 nautical miles off the east of the North Island, on Oct. 5. \"Safety remains the number one priority and salvage operations will only be undertaken when it is safe to do so,\" said Jobard. MNZ national on-scene commander Mick Courtnell said in the statement that variable winds and high swells had caused further oil leaks. \"This has resulted in some sticky tar balls coming ashore, and we have had a number of reports from members of the public,\" said Courtnell. \"Unfortunately, there is still a reasonably significant amount of oil on the wreck, out of reach of salvors. There is also still residual oil in the water, some of which is floating below the surface, and in the sand. This oil gets moved around with changes in the weather. \"Our teams will continue to clean and re-clean these beaches as long as we need to.\" Salvors have so far removed 167 cargo containers from the Rena, which was carrying 1,368 containers when it ran aground, although 86 containers were believed to have been washed overboard. About 30 little blue penguins were released in the Bay of Plenty region Thursday after cleaning and treatment for oil contamination. As of Thursday morning, 199 little blue penguins and 17 dotterels were still being cared for at the oiled wildlife facility, said the statement. Two senior officers of the Rena\'s Filipino crew have been charged in connection with the vessel\'s grounding and the resulting pollution.