I grew up by Lake Taupo. It has always been a beautiful place but just under the surface of what can be at times a perfectly still and mirrored lake is a bubbling cauldron of thermal activity. Lake Taupo is a huge crater lake. I myself have nearly drowned in it three times but Horomatangi hasn't managed to get me yet!
A taniwha in Lake Taupo.
This fierce taniwha lives by Motutaiko, an island in Lake Taupo, in an underwater cave on the western side. People used to avoid the island because Horo-matangi, if he saw them, would lash the water into high waves, overturn their waka and carry them down to his cave. This happened in good weather as well as bad.
At times Horo-matangi assumes the form of a reptile, or the form of a black rock. Some say he is an old man red as fire. His attendant Atiamuri, a taniwha in the shape of a man, was not dangerous in himself but would act as a decoy, attempting to lure unsuspecting travellers in Horo-matangi's direction. At twilight he would paddle a waka towards a settlement by the lake, going just near enough to be dimly seen. When the villagers called a welcome, he would disappear into the darkness and they would realise that Atiamuri had been trying to lure them to their death.
Many people have considered Horo-matango to be the custodian of the mana of Lake Taupo. Certain tohunga were his mediums, such as Te Ihu at Tapuaeharuru, who was said sometimes to live with him in his cave. As well, Horo-matangi is associated with two stone dogs high up on the Karangahape cliffs, on the lake's western shore. These dogs are never seen but may be heard howling on misty mornings. If paddlers on the lake were ever foolish enough to insult them by pointing their paddle or calling to them, Horomatangi would at once send a storm.
The Illustrated Encyclopedia of Maori Myth and Legend. Margaret Orbell Canterbury University press 1995. pg. 67