Manukau Harbour is the second largest natural harbour in New Zealand
by area.It is located to the southwest of the Auckland
isthmus, and opens out into the Tasman
Sea.The harbour mouth is between the northern head ("Burnett Head" / "Ohaka Head") located at the southern end of the Waitakere Ranges
and South Head at the end of the long Awhitu Peninsula reaching up from close to the mouth of the Waikato
The mouth is only 1800 metres wide, but after a nine kilometre channel it opens up into a roughly square basin 20 kilometres in width. The harbour has a water surface area of 394 square kilometres. There is a tidal variation of up to 4 metres, a very substantial change, especially since the harbour, being silted up with almost 10 million years of sedimentation, is rather shallow itself.
The harbour reaches into Mangere Lagoon, which occupies a volcanic crater. Auckland Airport
is located close to the harbour's eastern shore.
The harbour is popular for fishing, though entry to the water is difficult with few all-tide boat ramps; often local beaches are used.The harbour also houses five active sailing clubs, three on the southern side, one near Mangere Bridge
, and one on the northern side. Since 1988, there has been an annual interclub competition, hosted by each club in rotation.