The latest monthly regional tourism estimates, from the Ministry of Business, Innovation and Employment, showed Enterprise Dunedin was behind other centres in monthly and annual spending figures.
That put Enterprise Dunedin last on a list ranking the performance of 30 regional tourism organisations, and one of only three RTOs to record a decline.
Destination Kaikoura - bouncing back from the 2016 Kaikoura earthquake - recorded a 52% jump in August, while all other RTOs experienced increases of less than 20%.
The national average for August was 9% growth.
At the same time, annual growth for the year to August averaged 8% nationally, compared with the previous 12 months, but Enterprise Dunedin was also lagging behind, at just 6%.
Kaikoura again headed the pack, at 62% growth, while all other RTOs recorded increases of between 2% and 18%.
Otago Chamber of Commerce chief executive Dougal McGowan said the results were "not great" for the city and needed to be studied.
"It's a concern ... It doesn't make great reading."
Enterprise Dunedin, the Dunedin City Council's in-house tourism, marketing and economic development agency, was the "lead agency" responsible for the sector, he said.
It worked with partner organisations on initiatives designed to encourage growth, such as the city's Destination Plan, but "unfortunately in [August] it doesn't appear to have worked".
"I think it's going to be really important for the city [to study the results], because what we don't want to do is have those highs and lows.
"We need to understand what that data means so we can make sure we're not losing market share."
Enterprise Dunedin director John Christie said he was not concerned by the August result, as monthly figures tended to "bob around a little bit" depending on conferences, events and other variables.
The hosting of a Bledisloe Cup test in Dunedin last August, but not this year, was an example of what could change, he said.
He was more concerned to see Dunedin's annual growth rate was lagging behind the national average, "so we are looking at what that means and what's attributed to that growth", he said.
Some centres enjoying "exceptional" growth rates were starting from a low base, or enjoying the benefits of new infrastructure, or other factors, he said.
"We have to look at it in the context of measuring ourselves against those other tourism bodies that are reflective of the size of Dunedin.
"It could just be that we had a really soft month."
The figures also came as work on an independent review of Enterprise Dunedin was close to completion.
The review, which had already been signalled, was launched after Larnach Castle director Norcombe Barker called Enterprise Dunedin an "unmitigated disaster for tourism" earlier this year.
The review, by external consultant Martin Jenkins, had been due for completion in September, but council chief executive Sue Bidrose said yesterday a report was now expected next week.
It would be considered at the next meeting of the council's economic development committee, scheduled for November.
