Onepoto, Volcanic crater in North Shore, Auckland Region, New Zealand

Onepoto is a volcanic explosion crater, or maar, in the Auckland volcanic field near the approaches to the Auckland Harbour Bridge. Its tuff ring was breached by the rising Waitematā Harbour, so the crater floor is now a tidal lagoon. Since 1975 the reclaimed crater has formed Onepoto Domain, with sports fields, ponds, playgrounds and walks.

The crater formed about 185,000 years ago through volcanic activity and ranks among the earliest formations in the Auckland Volcanic Field. This long history makes it a window into the region's geological past.

The name Onepoto is Māori for "the shallows" or "low tide", referring to the tidal lagoon that formed when the Waitematā Harbour breached the crater's tuff ring. Since 1975 the crater floor has been reclaimed as the Onepoto Domain, used for sports fields, ponds, playgrounds and walks.

Onepoto Domain sits near the approaches to the Auckland Harbour Bridge, and the crater floor was reclaimed in 1975 for sports fields, so the ground is level and easy to cross on foot. Ponds, playgrounds and sealed bicycle tracks share the basin with the playing fields. Parts of the tuff ring were quarried away in the 1950s for Northern Motorway fill, so the rim is lower on those sides.

The crater's tuff ring was partly quarried away in the 1950s, and its fill went into building the Northern Motorway; in 1975 the crater itself was reclaimed for sports fields. The freshwater lakes that once filled Onepoto and neighbouring Tank Farm became tidal lagoons only after rising sea levels breached their tuff rings.