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 two cities of Auckland City and Manukau City and has a size of 6.6 km2 and a catchment of 34.5 km2, being considered to extend to just west of Onehunga (including where the Port of Onehunga is now situated). 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.
It is surrounded by the suburbs of Te Papapa, Southdown, Westfield, Otahuhu, Mangere East, Favona, and Mangere Bridge. The narrowest point on the Auckland isthmus is at Otahuhu, where the coast of the Mangere Inlet is a mere 1200 m from the Otahuhu Creek, which ultimately feeds into the Hauraki Gulf.
The Mangere Bridge crosses the western end of the inlet where it joins the main body of the Manukau Harbour. At this point the inlet is about 750 m wide. The Waikaraka Cycleway also travels along the northern shoreline of the inlet.
Portage Road is the location of one of the overland routes between the two harbours (and thus the Pacific Ocean and the Tasman Sea), where the Maori would beach their waka (canoes) and drag them overland to the other coast, thus avoiding having to paddle around Cape Reinga. This made the area of immense strategic importance in both pre-European times and during the early years of European occupation.