Canterbury Regional Council says it is not ruling out a prosecution against the fishing company Sanford, over Wednesday's oil spill at the Port of Timaru.
The council says the spill can be measured in the thousands of litres, however Sanford says it doubts it is that big, and it is still investigating to establish the size.
Sanford says one of its deep sea vessels, the San Enterprise, is the source of the spill and says it looks like a failure in an internal pipe on the ship caused the leak.
Council spokesperson, Kim Drummond, says a two-day clean-up has removed most of the oil and a dispersant has been put in the water to clear up the small amount remaining.
He says an investigation will now take place to establish the cause and decide if a prosecution is necessary.