Geology
The harbour is in fact a drowned valley system in marine sediments deposited during the Miocene. Recent volcanism in the Auckland volcanic field has also shaped the coast, most obviously at Devonport and the Meola Reef (a lava flow which almost spans the harbour), but also in the explosion craters of Orakei Basin and in western Shoal Bay. In periods of low sea level, a tributary ran from Milford into the Shoal Bay stream. This valley provided the harbour with a second entrance when sea levels rose, until the Lake Pupuke volcano plugged this gap.
The current shore is strongly influenced by tidal rivers, particularly in the west and north of the harbour. Mudflats covered by mangroves flourish in these conditions, and salt marshes are also typical.
Read more about this topic: Waitemata Harbour