Taniwha are huge water lizards spoken of in Polynesian mythology. They each have many manifestations, but some are more powerful than others.  The form taken generally reflects the current environment of the taniwha. While in the ocean, taniwha often appear to people in the form of whales or sharks, sometimes together in a school. While in rivers and lakes or inland waters, they may be as large as a whale, but generally take on the form of a gecko or tuatara lizard. And, some in lakes appear, curiously, as a floating log, which reveals itself a taniwha by either moving against the current or not moving in a current. 
Taniwha Spirits of the Water: Guardians and Monsters
Taniwha are sometimes called the spirits of the water, since the majority of them live in either the oceans or within inland waters. While some can move over, or sometimes through, the earth, they generally settle in watery homes. 
Depending on time and circumstances, taniwha might save those thrown from ships or fallen into the sea. Of course, at other times, the taniwha might be the reason the person is dragged to the depths and drowned.  Taniwha can be very vengeful dragons and when angered turn outright deadly en masse. 
Taniwha in Tradition
Taniwha the wrathful dragons of Polynesian Mythology.
© Donna Quinn.
According to traditions across New Zealand, taniwha carved harbors and opened up channels to the sea throughout the islands, even creating new mountains and canyons inland on their travels. Yet, it is also known that such powerful beings also cause destruction. Some have been known to cause landslides, and some natural disasters are still attributed to particularly angry taniwha. There are also many cases of humans battling taniwha, generally as part of war or to protect the local population from a vengeful taniwha that cannot be appeased, and always the humans win with numbers, despite the mythical powers of the taniwha. 
In Māori tradition, most taniwha are associated with humans, because every people have a taniwha of their own. Specifically, many famed taniwha arrived from Hawaiki, the mythological homeland of the Maori people, because they traveled with the waka, or canoe, and settled in Aotearoa (the new land) with the descendants of the vessel's crew.  Taniwha, in general, behaved benevolently towards their own people, acting as guardians, sometimes even warning the people of storms, attacks, and so on. As part of guardianship, however, the taniwha also ensured that their local people followed the tapu (taboo, restriction) law placed on them, which sometimes included restricted foods and limited allotments of gathered resources. Should a protectorate of a taniwha break any tapu, the taniwha would be the guardian that enforced it, lashing out until the people made an appeasement and apology. 
Because taniwha operated as both protectors and menaces, any place that was known to be home to one of them is given a particular respect. Often these places are inaccessible to humans anyway; places of strong currents or dangerous breakers tend to prevent people from traveling. However, should one travel over the home of a Taniwha, it is best to have an appropriate offering and chant ready to appease the creature, who will guard hearth and home ferociously. 
Rarely, a person who had associated with taniwha might become one after death, to continue to help and to protect people. A person could be associated to taniwha in many ways: the person may be a medium for the taniwha's communication, the person may have married a taniwha, or perhaps the person formed a bond of friendship with one.
For more information on footnotes and references, please see the bibliography.