The supermoon on Monday evening is expected to disrupt ferry crossings in Auckland.
On Tuesday, Wednesday and Thursday some afternoon services will be replaced by buses due to lower than normal tides.
The supermoon causes both higher and lower tides, and when the tide is at its lowest the water level won't be high enough for ferries to travel to and from Half Moon Bay.
Monday night's supermoon is the first of three expected over the next few months.
NASA is calling it the 'Supermoon trilogy', with further supermoons expected on January 2 and January 31 next year.