It is a sandspit estuary, located on the north-eastern coast of the Auckland Region north-east of Matakana, and empties into the Hauraki Gulf.

High numbers of Scutus breviculus, octopuses and Australasian sea cucumbers live in the estuary.

[5] The name Whāngateau was a traditional Māori language name for the harbour, and refers to the strong tidal currents in the estuary.

[5] The harbour and surrounding Mahurangi area was first settled in the 14th century by Māori, descendants of the Moekākara, Tainui, Arawa migratory canoes.

[7] Between 1942 and 1963, 380,000 cubic metres of sand were mined from the Mangatawhiri Spit, leading to coastal erosion at Omaha.