An oil spill team worked fast to clean up a 2ha oil slick in Napier's inner harbour.
The spill, thought to be from the bilge of a boat, was broken up by using another boat to agitate the water.
The boatie responsible for the spill, which was found about a mile off-shore from the harbour on Monday, was nowhere to be found.
Hawke's Bay Regional Council staff estimated it to be about 10 litres of oil.
Regional council regional on scene commander Bryce Lawrence said it took them about an hour to disperse the spill.
"We just drove through it for half an hour just to break it up," he said. "That was probably the largest we've had for a few years, but that's not a dramatic statement. It was a relatively small amount of oil.
"It was just a patch of oil in the water. There were no indications as to who it was. It was disappointing, had it occurred in here [the harbour] there would have been a few upset people."
Coincidentally, the regional council had an oil spill response drill take place yesterday in the harbour.
Equipment such as booms and frame tanks were used for a mock scenario in which 10,000 litres of diesel oil had been spilt in the inner harbour.
Mr Lawrence said marine oil spill responses were broken down into three categories.
A tier one spill was usually dealt with by the boat involved and the spill may not have even reached the water.
Tier two were larger spills requiring regional staff, for which the response was valued up to $250,000. Above this threshold were tier three spills that required attention from national response members. Mr Lawrence said Monday's spill was a tier two.