With an area of 70 square miles (180 km2), it connects the city's main port and the Auckland waterfront to the Hauraki Gulf and the Pacific Ocean. It is sheltered from Pacific storms by Auckland's North Shore, Rangitoto Island, and Waiheke Island.
The name Waitematā means "Te Mata Waters", and refers to Te Mata (Boat Rock), which lies in mid-harbour off Kauri Point. A popular translation of Waitematā is "The Obsidian Waters", referring to obsidian rock (matā). Another popular translation, derived from this, is "The Sparkling Waters", as the harbour waters were said to glint like the volcanic glass obsidian. However, this is incorrect, as grammatically Waitematā could not mean this.
The spelling Waitemata (without a macron) is common in English.
The harbour is an arm of the Hauraki Gulf, extending west for eighteen kilometres from the end of the Rangitoto Channel. Its entrance is between North Head and Bastion Point in the south. The westernmost ends of the harbour extend past Whenuapai in the northwest, and to Te Atatu in the west, as well as forming the estuarial arm known as the Whau River in the southwest.