Environment Canterbury staff working to clear an oil spill at Timaru's port have placed a boom in the water.
About 40 staff have be working since midday on Monday to contain about 40 litres of light fuel oil that leaked from a boat at PrimePort Timaru.
Canterbury regional harbourmaster Jim Dilley says the team have been removing oil from the water and expect most of it to be gone by Monday night.
Mr Dilley says the boom will remain in place overnight to catch any oil missed under the wharf and any further oil will be removed on Tuesday.
An investigation may be launched, he says.