A foul stench being emitted by Dunedin's wastewater plant has its manager stumped.
Nearby residents have made two dozen complaints about the vomit-inducing smell around the Tahuna plant, but there is no solution in the wind.
It has been off and on again since last Wednesday - a rotten egg smell coming in waves across part of south Dunedin.
Plant manager Chris Henderson said the filters intended to strip out the hydrogen sulphide gas were not working, or were overloaded.
He said he was baffled, because his staff had fixed the filters - yet the stench had returned.
External contractors were on site helping staff.
Mr Henderson said all he could do was apologise wholeheartedly and that fixing the problem was his top priority.
"It's a primary concern because we have schools, we have a golf club, we've got a bowling club, this plant is situated 20 metres away from residential properties.
"Our own goal is to have no odours emanating and annoying people."
Mr Henderson hoped the stench would be gone in a few days.