[1] The Porirua Harbour formed when westward flowing rivers were drowned by rising postglacial sea levels approximately 10000–14000 years ago.

[2] There is a tradition that the 1855 Wairarapa Earthquake caused tectonic uplift in the Pāuatahanui Arm of the inlet, changing the shoreline and reducing its navigability.

[4][5] The line no longer followed the curves of the shoreline bays north of Porirua, and three shallow lagoons on the land side of the new causeway were created.

When State Highway 1 was re-aligned and straightened in the 1970s to run alongside the rail line, these lagoons were partially filled in.

[1] There are also fishing spots at Tokaapapa Reef (or Grandfather rocks) off Plimmerton, Mana Island and Hunters Bank.