People in Motueka are being advised not to collect shellfish or fish on the wharf after a diesel spill into the harbour and estuary was discovered yesterday.
About one-hundred litres of diesel, originating from Port Motueka, entered the immediate port area and through tidal flows into the Motueka estuary.
Maritime New Zealand advised the Tasman District Council that natural dispersion of the spill was appropriate.
Marine life was unlikely to be affected, but people were being advised to avoid fishing in the vicinity as a precaution.
The council's spokesperson Chris Choat said it was not known how the spill occurred but a full investigation would be launched.
He said council officials and the Regional Oil Spill Response team would continue to monitor the situation.