Cr Niki Gladding said she would be joining a protest against the plan on Wednesday.
She said councillors were told of the possibility at a workshop on Thursday.
They were told it was proposed in response to issues with the district’s wastewater treatment plant’s disposal field.
The most recent issue, she said, was the threat of bird strike at the nearby airport runway from an increase in waterfowl landing at the disposal field at the Shotover wastewater treatment plant.
The Queenstown Lakes District Council (QLDC) is also in Environment Court mediation with the Otago Regional Council which is seeking an enforcement order after consent breaches at the disposal field, including surface ponding of wastewater and the discharge of effluent outside the consented disposal field area.
Cr Gladding said QLDC chief executive Mike Theelen informed councillors on Thursday of the proposal to allow 12,000 cu m of treated wastewater to be discharged into the Shotover River daily, instead of on to the disposal field, as a means to address the bird strike concern.
This could be done using special emergency powers under the Resource Management Act.
"It's a massive step, and I think the chief executive needs to be very careful because he's taken the step on his own at this point," Cr Gladding said.
"He needs to use those powers carefully . . . because we could be prosecuted if we use Section 330 [of the Resource Management Act] when we shouldn't have."
Section 330 of the RMA authorises consent authorities to undertake emergency works on both public and private property.
Cr Gladding said it would be a good option if the council paused such moves.
"The chief executive doesn't have a mandate from council [to do this]. Councillors were given no option at all."
She also expressed concern about whether Ngāi Tahu had been involved in the process at any stage, particularly given the fact Mr Theelen indicated to councillors that the action would begin this week and could last for several years, she said.
"I'm really concerned that QLDC is deliberately failing to disclose what it's planning to do so that people can't get to stop it.
"They do need to stop. They do need to give everyone a chance to feed in and give some input . . . and they should not be discharging to water [this week]."
When asked for a comment, a QLDC spokesman said more would be revealed to the public on Wednesday this week.
The council is scheduled to speak to media at the treatment plant that day.
A new protest group called Queenstown Community Action, which says on Facebook it expects transparency from the council and has concerns about the management of the wastewater system and the risk of environmental damage, has announced it will host a protest at the same time and place the council is scheduled to speak on Wednesday.
Protest group organiser Nikki Macfarlane said they formed the group as they were unhappy with the way the QLDC had treated the public on this issue, which "raised all kinds of red flags".
Cr Gladding said she was aware of the group and would be joining the protest.
Queenstown Lakes District Mayor Glyn Lewers said yesterday the matters Cr Gladding discussed came from a workshop which was supposed to be confidential.
"Those discussions were held in public excluded for a reason, and so I'm not going to obviously delve into the subject matter.
"I'm pretty confident that everything will be presented to the public on Wednesday and they'll have all the information they need."
On Friday, the QLDC general manager Tony Avery said the plant’s performance was monitored daily, and results from both on site monitoring and external laboratory tests demonstrated that "the treatment standard is consistent with the plant’s resource consent conditions".
“The disposal field is separate to the treatment plant and is not relied on as part of the wastewater treatment process.
"This means that water flowing into the disposal field is treated to a standard appropriate for the downstream receiving environment, in this case the Shotover and Kawarau rivers."
