Environment Southland staff are investigating the cause of a large oil slick which has covered the Otepuni Creek in Invercargill.
The slick, believed to be engine oil, is concentrated in several spots on the creek over an area equivalent in size to two city blocks near the Leven St bridge in the city centre.
Environment Southland compliance officer Chris McMillan said staff responded to a call from the public yesterday morning, but the spill may have happened on Monday.
It is not known yet how the oil got into the creek, but it is believed it may have been poured into a stormwater drain which flowed into the creek. A search of the local drains had so far failed to locate the original source of the oil.
Inquiries were continuing but it might be difficult to find the source, he said.
"Engine oil is worse than some other oils as it doesn't evaporate and can linger in the stormwater system for months."
Oil-absorbent booms, mats and pillows had been used at several points along the river to remove as much of the remaining oil as possible before it entered the Waihopai arm of the New River Estuary, he said.
No wildlife had been affected by the spill so far.
Mr McMillan said enforcement action could be taken if the offender was identified and he asked anyone with information to contact Environment Southland's compliance staff on 0800-768-845.
Engine oil should be disposed of in a proper manner.
Most landfill sites had an oil disposal service and many trade practices used recyclers to collect their waste oil, he said.
