It is perhaps better described as a silty arm of Whangārei Harbour, located 10 kilometres (6 mi) due south of Whangārei.

Its average width is some 4 metres (13 ft), but the silty nature of its course means that the stream itself is far narrower.

The New Zealand Ministry for Culture and Heritage gives a translation of "good stream" for Mangapai.

[1] "Place name detail: Mangapai River".

This article about a river in the Northland Region is a stub.