Lake Brunner (Māori: Moana Kotuku) in Westland on New Zealand's South Island has been the source of an unusual and persistent body of light-phenomena reports stretching from the first European settlement in the 1860s to the present day. The lake sits in dense podocarp-beech rainforest at the base of the Southern Alps, and is subject to some of the most extreme rainfall in the country (more than four metres annually) along with rapid temperature inversions. For more than 150 years, residents of the surrounding settlements — Moana, Mitchells, Iveagh Bay, Te Kinga — have reported slow-moving orange or greenish orbs travelling above the lake surface, typically at night and most often in the autumn months when temperature inversions are most frequent.
The Ngāi Tahu tradition of the district identifies the lights as wairua (spirits) associated with the taniwha Kotuku, who gives the lake its Māori name. European sighting reports are consistent: a 1887 Grey River Argus account described lights 'of no ship or light-house' hovering above the southern end of the lake; a 1932 West Coast Times piece reported two Mitchells farmers watching a 'yellow fire the size of a hay bale' move across the water from the Iveagh Bay shore; and in 1967, a State Hydro-Electric Department survey team in tents at the Kumara Junction reported multiple orange lights for three nights in succession. As recently as 2018, a kayaker photographed a slow-moving greenish-white orb above the lake surface at dusk; the photograph was published by the Greymouth Star and analyzed at Canterbury University, which could not identify the object.
Ball lightning, foxfire, swamp gas, and reflected aurora australis have all been proposed as explanations; none fits the duration, altitude, colour, or stable shape of many reports. Lake Brunner sits on a series of low-grade seismic faults and its water column produces significant methane ebullition, which may explain some of the surface manifestations. Other observers insist the lake's paranormal character is more than geophysical, and the Ngāi Tahu rāhui concerning the Moana Kotuku spirit beings remains in force.