The Bay of Plenty Regional Council is investigating an oil spill in Tauranga Harbour.
A passing pilot reported an oily sheen near the Marine Precinct to the regional council's pollution hotline Monday around 2pm.
After enquiries, regulatory compliance manager Stephen Mellor said in a written response six staff were on-site "quickly", both on land and on the water.
An absorbent boom was used to help clean up minor residual sheen.
Mellor said they were able to track the oil back to two possible sources by 4pm.
The amount and type or types of oil are yet to be determined through an analysis of the samples taken.
"Any oil in the water is completely unacceptable, however, we don't expect any wildlife to be impacted as a result of this spill," Mellor said.
There are two agencies involved in the response.
The regional council is responsible for responding to the initial spill, the investigation and enforcement functions.
Maritime New Zealand (MNZ) is responsible for commercial vessel operating procedures, and health and safety requirements. They also oversea the Marine Pollution Response Service which is expected to provide advice and additional resources for the spill as needed.
"Light oils like diesel fuel and synthetic hydraulic oils spread widely and evaporate quickly, which can make them hard to collect and remove from the water," Mellor said.
"The exact type, or types, of oil spilt will be determined by later analysis of samples taken at the time."
As the matter was under investigation, the council would not comment on the sources of the spill or likely volume of oil spilt.
A Maritime New Zealand spokesman said the regional council was leading the response and advised the government agency, as it is required to do, at about 4.50pm yesterday.
There are three levels of maritime oil spill response which are provided for in the Maritime Transport Act 1994.
Tier one is cleaned up by the people who spilled the oil, tier two is managed by the regional council, and tier three is a national response led by Maritime New Zealand.
This spill was classed as tier two, the spokesman said, and the council advised Maritime New Zealand so if the spill became bigger, support from other areas was available
"Bay of Plenty Regional Council has advised Maritime NZ it is working with the owners of the two vessels to prevent any further leaks."
Under the Maritime Transport Act 1994 the polluter pays all costs from an oil spill response and subsequent clean up.