Oil company Mobil is being prosecuted over a spill in Tauranga harbour while a ship was re-fuelling.
Bay of Plenty regional council said it had lodged charges under the Resource Management Act (RMA) and expected proceedings to begin next month.
The 1500 litre oil spill in April coincided with bad weather that spread the oil slick around and slowed down the clean-up.
Mobil said it would reimburse the council for $1.79 million including $836,000 in clean-up costs. The company said the money had been paid.
The company said it deeply regretted what happened, and had fully co-operated to help restore the harbour.