Taniwha is the Māori name used for “monster”, but is most commonly used to describe enormous vaguely serpentine lizard-like creatures in Māori folklore. They are described as large green-scaled reptilian animals, comparable to a monitor lizard or crocodile, that inhabit the sea, as well as rivers, lakes and pools. In some Māori folktales, they are protective guardians or kaitiaki, while in others, they are dangerous man-eating carnivores. They are often mistaken for floating logs and are rather well camouflaged. There are many legends of them being killed by folk heroes, analogous to European folklore of dragons being slain by heroic knights.

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A common theory as to the origin of taniwha myths is exaggerated memories of vagrant saltwater crocodiles. Vagrancy is a biological term for individual animals being found far outside their accepted range, usually as a result of getting lost. Like the taniwha, saltwater crocodiles are large, green, aggressive scaly reptiles that can both live in salt and freshwater environments.

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There have actually been examples of saltwater crocodiles swimming to New Zealand, most famously in the North Cape in 1970, which was spotted by the ship M.V. Parera. In broad daylight, they witnessed a 15 foot long crocodile swimming the opposite direction only 20 feet from their boat. It was thought to have either swam their from Australia or Vanuatu, both roughly the same distance to New Zealand. Individual saltwater crocodiles have also been observed going to other locations far outside their typical range, like Fiji, the Maldives, Nauru, Iwo Jima, The Marshall Islands and even the northwest coast of Honshu.