Origin: Maori (Māori) Mythology, New Zealand
About Niua / Niwa / Hiwa
Niwa, also regarded in different traditions as Niua or Hiwa, is a taniwha that inhabits Hokianga Harbour as one of the guardians. He is the north head of the harbor, and Araiteuru (Āraiteuru) is the south head. 
In some variations, the great explorer Kupe left Niwa behind to guard the harbor, since Niwa was once of his taniwha pets. Should any invaders try to land on shore, Araiteuru (Āraiteuru) and Niwa would thrash their terrible tails and cause the ocean to churn, leaving the invaders shipwrecked. 
- Orbell 13
- Gregory - The Hokianga Harbour. Link defunct: <http://www.tki.org.nz/r/farnet_new/te_kupenga/hokianga.php>
For more information on footnotes and references, please see the bibliography.