By Katie Todd of RNZ

A Queenstown community group is alarmed about a sharp spike in Escherichia coli levels in the Shotover River, just downstream from the town’s troubled wastewater treatment plant.

Otago Regional Council is investigating a high reading that Queenstown Lakes District Council said was unrelated to the plant’s operation.

Queenstown Lakes District Council (QLDC) has been pumping treated effluent into the river for more than a year, following issues with the plant’s disposal field on the Shotover Delta.

Last month, councillors agreed to seek a 35-year consent to keep pumping treated wastewater into the Kawarau River while a longer-term solution was found.

Monitoring data on the QLDC website showed Escherichia coli (E. coli) levels reached 2100cfu (colony-forming units) at a site near the discharge point on March 10, which was eight times above the council’s annual average consented limits and almost four times higher than safe swimming limits.

Right before the treated wastewater left the plant, it returned a reading of 25cfu, while levels upstream in the river ranged between 1-490cfu throughout March.

In a statement, Queenstown Lakes District Council said the spike could have been a compromised sample or isolated contamination, noting E. coli results varied because of wildlife and weather.

Queenstown Lakes Community Action member Nikki McFarlane said the data was strange and the spike was big.

She said the council should be more upfront.

“We’d like to see QLDC much more proactive in giving explanations for when there’s high levels or of contaminants. I think it would go a long way to have public confidence if we actually did see an explanation, if there was a logical explanation,” she said.

Otago Regional Council confirmed it was investigating the March 10 reading.

“We can’t comment on the cause while an investigation is underway,” the council said.

As part of its own regular monthly sampling it had also taken samples over 17 different days in March, the council said.

McFarlane said government water quality guidelines showed water with E. coli levels above 550cfu was unsafe for swimming, yet Queenstown Lakes District Council did not put up any signs warning people to avoid the river.

Queenstown Lakes District Council told RNZ the location in question was not a common recreational bathing area and by the time the results were returned “whatever caused the elevated result was unlikely to be present”.

McFarlane said the council should still let people know.

“For us, it’s their responsibility, even though they’re not managing the rivers per se, just making sure that the public understand when the river is safe and when it’s not,” she said.

“We’ve asked for that before, to put up signage, to put a message on the website so people know not to go swimming at that particular area. We haven’t had any positive response.”

The Queenstown Lakes District Council website showed at least three other spikes in contaminant levels over the past year, which the council attributed to a disruption to the treatment plant’s control system, upgrades combined with cold weather and rainfall.

McFarlane said the community group was concerned about the possibility of untreated sewage ending up in the water.

Her group was preparing to take part in an Environment Court hearing challenging the retrospective consents that the council lodged after first discharging treated wastewater into the river.

“It’s not a case of if they have another operational problem at the plant, it’s when. And because we no longer have any barrier between the plant and the river, when they have another operational failure, then that is going to go straight into the river and that’s really concerning,” she said.

Queenstown Lakes District Council said the plant was performing as expected, within consented limits and there was no additional action required or planned.

“Our primary interest is in the quality of the treated wastewater leaving the plant as this is the only aspect entirely within our control,” a spokesperson said.

Last month, the council’s decision to lodge a 35-year consent application came despite Ngāi Tahu stating that the direct discharge of human waste to natural water was “abhorrent” and contrary to tikanga.

– RNZ