It is located on the north-eastern coast of the Auckland Region near the town of Warkworth, and empties into the Hauraki Gulf.

[1] The modern harbour formed approximately 7,200 years ago at the end of the last glacial maximum, when the forested valley was flooded by rising sea levels.

[2] Land use within the harbour's catchment basin has been changing, and as of 2013[update] models predict an increase in sedimentation.

[3] A number of settlements are found along the shores of the harbour: Mahurangi West, Pukapuka, Pohuehue, Snells Beach and Scotts Landing.

Sea captain John Sullivan moved to the area in the 1870s, settling at Otarawao and marrying Merehai Kaipuke, a Ngāti Rongo woman of high birth.