Queenstown Lakes District Council maintenance and operations manager Erin Moogan said a blocked sewer main caused sewage to overflow from a manhole on the lakeside walking track near Loop Rd in Kelvin Heights.
The council was notified about 10.45am, and contractors were at the scene within 15 minutes.
The overflow was caused by historical damage to the pipe by a third party who had glued a piece of road sign over a hole, Ms Moogan said.
That had allowed tree roots to enter the pipe, causing the blockage.
Contractors isolated the leak, removed the patch and repaired the pipe, and the wastewater network was restored by 12.30pm.
"The site was cleaned and disinfected, water samples taken from the lake and ‘no swimming’ signs were put up as a precaution," she said.
"As the pipe has now been professionally repaired to an industry standard, it is very unlikely that another blockage will happen at this site."
