The pedestrian causeway, made of manuka logs and buried in mud, was discovered at the Dunedin City Council's Wall Street development.
The 14m by 4m causeway was a "significant site" not just for the city, but also New Zealand, Historic Places Trust (HPT) regional archaeologist Dr Matthew Schmidt said.
"There hasn't been a find like this in New Zealand."
Dating back as early as 1850, the causeway would have been built by early settlers not long after "stepping off the boats".
The preferred option, based on archaeological finds overseas, was to leave the causeway where it was, he said.
A report on the future of the causeway will be presented to the council tomorrow by Wall St project manager Dave McKenzie, the author of the report.
Mr McKenzie would not comment on possible options, but said the causeway was "creating some challenges".
The findings of the report would also be discussed with the Historic Places Trust, Mr McKenzie said.
"At this stage, we are unsure what the next step is," he said.
Trust Otago Southland area manager Owen Graham said two experts from Wellington would analyse the site.
"They will will give specialist advice in terms of managing the resource."
Their findings would be presented to the council in conjunction with the report, he said.
Southern Archaeology archaeologist Peter Petchey said a decision on the future of the site would be welcome, as some of the wood had deteriorated since the discovery.
