A piece of Dunedin's history lies buried under the city's latest highway development.
Contractors working on the Caversham Highway uncovered a pre-1900 water reservoir carved into sandstone within the Lookout Point Reserve.
But they have since built over it.
The New Zealand Historic Places Trust (NZHPT) is investigating the structure's origin.
NZHPT Otago/Southland area manager Owen Graham said the reservoir was unique.
''There are no similar features recorded in Dunedin so it is uncommon. Indications are that it probably dates from before 1900.''
Its burial was the only practical option, he said.
''It is an acceptable outcome to either relocation or demolition and removal.''
Mr Graham said an archaeologist was authorised by the trust to work with the New Zealand Transport Agency (NZTA) on its multimillion-dollar Caversham project.
The archaeologist, Cathryn Barr, was investigating the reservoir, as well as any other archaeological matters arising from the development.
She would present a final report to the trust once the roading project was complete, Mr Graham said.
The reservoir discovery earlier this year was publicly announced by the NZTA this month in its latest update of the project.
It said ''what appeared to be'' an historic reservoir was uncovered during earthworks in the Lookout Point Reserve.
''The reservoir was carved into the natural sandstone bedrock with clean water channelled through a fracture in the rock. Even the steps appear to have been carved with hand tools into the sandstone.''
The site was photographed and ''recorded'' for the trust to investigate, the NZTA said.
Project manager Simon Underwood said the NZTA had archaeological authority in respect of the project and followed all protocols set by the NZHPT.
''Once we excavated it, photographed it, recorded it and had a report prepared we were free to cover it back up,'' he said.
The reservoir could not be moved and the highway could not be diverted around it, Mr Underwood said.
