The 19th century bridge, over the Taieri River on Sutton-Mount Ross Rd, was destroyed when floodwaters swept through the area on Saturday.
The bridge was undergoing strengthening work and only recently reopened to heavy trucks, but scaffolding remained in place.
Local residents claim debris caught in the scaffolding contributed to the bridge's demise.
Dunedin City Council acting group transport manager Merrin McCrory said the scaffolding was necessary because the remedial work was not complete.
''The scaffolding was in place as the work was not complete,'' she said.
''Work was still under way to complete strengthening from a five-tonne weight restriction to a 19.5-tonne weight restriction, and scaffolding was required to complete this work.''
An engineering consultant was assessing the likely reason for collapse and the council would not speculate.
''The restoration of the bridge is a DCC project and the collapse is very disappointing for everyone involved,'' she said.
''We met with Heritage NZ and engineering consultants to look at the bridge yesterday.
''The consultants will prepare a report assessing the likely cause of the bridge's collapse.
''We don't have a timeframe for the report yet.
''The report will also give a high-level assessment of the work and costs involved to repair the bridge so that we can make a decision about how to proceed. We cannot speculate on the cause of the collapse until we receive the report.''
The council was working with contractors and Heritage NZ to secure heritage components or salvage them so they could be stored.
The loss of the bridge was a blow to local residents.
''It's a big landmark for the town,'' one commented.
''There's a lot of stories under that bridge.''
Sutton farmer Kathy Tisdall, whose land borders the Taieri River, said the collapse of the bridge was a huge loss for the community.
''You see pictures [of it] in ... people's travel photos, and wedding photos - all sorts of things,'' she said.
''It is - was - a nice bridge.
''It's very sad to see it how it is.''
