Westland Milk Products has been fined after an accidental oil spill into the Hokitika River.
The West Coast Regional Council issued an infringement notice after investigating the September 30 incident in which a quantity of canola oil entered the river via a stormwater drain.
Westland Milk Products environmental manager Chris Pullen said most of the oil was contained on-site, and of that which did escape nearly all of it was confined within the floating booms placed in the river and was then removed using tractor-driven sucking equipment and scoop nets.
Oil deposits were also removed from along the shoreline, Mr Pullen said.
"However, after talking to whitebait fishers downstream, we confirmed that some oil did drift downstream and was visible in their nets, which impacted on their activities. This is regrettable and the company apologises for the inconvenience caused."