Canterbury Regional Council says it's confident a diesel spill from the fishing boat moored at a wharf in Lyttleton Harbour has had very little impact on the environment.
Harbour master Jim Dilley says they received a call early on Sunday morning from the crew of the Ocean Breeze saying the vessel had been leaking oil.
He estimated up to 150 litres of diesel escaped, but said much of that had evaporated in the sunny weather or been soaked up using absorbant booms and pads.
Mr Dilley says he expects the impact on the environment to be minimal.
"It's not over an abundantly habited area, it is a commercial working area. There's lot of activity there, it's not quiet and not the sort of place wildlife would like."
Mr Dilley says once the oil has been pumped from the leaking tank, work will begin on finding the cause of the leak.