Mangere Inlet is an arm of the Manukau Harbour, the southwestern of the two harbours of Auckland, New Zealand and itself an arm of the Tasman Sea. The inlet lies between the Auckland isthmus and South Auckland, and has a size of 6.6 km2 and a catchment of 34.5 km2, being considered to extend to just west of Onehunga. It is an environment highly modified by land reclamation and human uses, with the northern shoreline especially affected. However, the inlet also acts as a natural sedimentation sink, thus being especially at risk of contamination.

The 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.