Crews are urgently trying to fix an overflow of partially treated wastewater that has entered a Queenstown swamp.
The effluent had spilled over the top of an oxidation pond at the Shotover Wastewater Treatment Plant.
Queenstown Lakes District Council confirmed it had reached a small section of nearby natural swamp and Shotover Delta Road was closed as a precaution.
Acting property and infrastructure general manager Simon Mason said no contamination was believed to have reached Shotover River.
"Crews are currently onsite working to resolve the issue and determine exactly what has caused the pond to overtop," Mason said.
Otago Regional Council's pollution team was notifed, and compliance officers were investigating the overflow.
Nearby walking tracks in the area remained open to the public.
The council confirmed the spill was not connected to ongoing repairs of the plant's aeration grids, which were causing an odour to linger in the area.
Mason said work to fix the aeration grid was under way with spare parts sourced from the United States being installed at the plant.
"As these repairs are made, the biological process treating the wastewater will progressively recover over the coming days and weeks and we hope to see the end of odour in the area soon after that."