In Māori mythology, the supernatural creature that may guard a water body or appear as a shape-shifting monster is a taniwha.
Taniwha are powerful beings associated with deep river pools, caves, the sea, dangerous currents, and deceptive breakers. Their appearance is not fixed. A taniwha might resemble a whale, shark, gecko, tuatara, or even a strangely moving log. This flexibility is why translating taniwha simply as “monster” misses much of the concept.
Many taniwha act as kaitiaki, or guardians, for particular people, places, or tribal groups. They may warn of enemies, protect travellers, or punish breaches of tapu. Other stories portray them as predators that abduct or eat people. Whether protective or dangerous often depends on the relationship between the being and the community, and on whether proper respect is shown.
The word is singular and plural in Māori. It is also related to Polynesian forms such as Tongan and Samoan tenifa, words connected with dangerous sharks or sea monsters. The guardian taniwha Ureia, linked with the Hauraki people, is one well-known example.