Whangarei Heads ship spotters were alarmed to see what looked like "black gunk" streaking down the side of a vessel at Northport after its decks had been sluiced down.
Closer inspection by Northport and Northland Regional Council (NRC) staff on Tuesday showed it to be old, solidified concrete, not material washed off the decks during a fire equipment test on Monday night.
After the Marshall Island-registered cargo ship Western Alberito had docked, Maritime NZ requested a routine safety check, including running sea water through the fire pumps, hoses and the ship's cooling system.
Northland deputy harbourmaster Chidambaram Surendran said the NRC had responded to calls about what could be a possible harbour pollutant on the ship's side but it was not an environmental hazard and was unrelated to the sluice-down. Nor was there any debris or other material in the water following the equipment drill, Mr Surendran said.
