After the spill in Athol St, in which between 100 and 500 litres of wastewater reached Lake Wakatipu via Horne Creek, the Queenstown Lakes District Council said cameras would be used to inspect the sewer network.
The blockage was caused by two pavers which had become wedged in the pipes at two separate locations. The pavers were removed on Monday night by Veolia Water staff.
QLDC infrastructure and assets general manager Erik Barnes said the council was not sure how the pavers got into the system.
When asked whether they could have been deliberately placed there, Mr Barnes said ''anything is a possibility''.
''But I hope human nature isn't as malicious as that.''
Athol St, Horne Creek and the lake foreshore were all disinfected on Monday night and some of the spill started creeping down KFC's drive-through, which was closed for a time while it was disinfected.
Sewage did not enter any buildings.
When approached, KFC declined to comment about the spill.
Mr Barnes said the disinfectant used ''neutralises quite rapidly'' and any ducks and fish life in the area would not be harmed.
A week ago, about 5000 litres of wastewater flowed into Lake Wakatipu because gravel and stone, possibly from construction debris, had blocked a pipe, forcing the liquid up through a manhole.
Mr Barnes said it was highly unlikely Monday's blockage was related to the earlier blockage and a full inspection of the system under the CBD had been arranged.
If the council managed to find who caused the pavers, gravel and stone to be in the pipes, they could be liable to pay costs.
