Dead birds have been found up to 80m from a council-run wastewater treatment plant where avian botulism has been confirmed, though the council believes the disease is contained to the site.
A Dunedin City Council spokeswoman said this morning council staff believed the outbreak, which has killed more than 1000 birds, had not spread.
" . . . far as we are aware, the botulism outbreak has not spread beyond the wastewater treatment plant."
The disease is not known to transfer from birds to humans.
Otago Fish and Game confirmed this morning it had found dead birds up to 80m from the treatment plant.
It was monitoring other water sources in the area, including the Waikouaiti Estuary and the Hawksbury Lagoon, a spokesman said.
The DCC on Monday identified avian botulism, a disease that causes paralysis in birds and often kills them, at the Waikouaiti wastewater treatment plant, which is about 1km from the Waikouaiti Estuary.
"Avian botulism is a known risk at certain water bodies [including treatment ponds] across New Zealand," the council said in a statement.
"The bacteria occurs naturally in soils around ponds and wetlands and is also found in oxidation ponds. It is harmless until certain environmental factors occur, such as low oxygen and warm temperatures."
The medical officer of health had confirmed the risk to human health was "very low" and "botulism in wild birds was not know to cause botulism in humans" , the statement said.
A council spokesman said the outbreak at the plant had nothing to do with the way it was operated.
The outbreak is unrelated to the recent avian influenza outbreak at a North Otago egg farm but is being treated as a significant animal welfare issue.
Otago Fish and Game chief executive Ian Hadland said the majority of the dead birds collected so far were native paradise shelducks, although the disease had also struck native grey teal, mallard, Canada geese, black swans and black-backed gulls.
He said the organisation was unsure whether the operating conditions of the wastewater treatment plant led to the outbreak.
"It's part of our questions for the city council, actually.
"So we'll be making those inquiries [about the wastewater treatment plant] to find out what was it that actually led to this situation."
The council said it had "activated its management plan for collecting and disposing of dead birds and will continue for the next few weeks".
"This should help stop the spread and break the chain of infection."
Avian botulism has killed an estimated 25,000 birds in the Auckland/Waikato region in some years.
Mr Hadland said outbreaks of avian botulism were more common in the North Island, but this could be a problem that occurred again in the South soon due to climate change and declining water quality.
"So for example, if you had a low oxygen event in Hawksbury Lagoon or Lake Waihola or one of those other lakes or wetlands or water treatment ponds, then this could break out further south again."
Such outbreaks were of great concern to the organisation, particularly in light of the avian influenza outbreak last month, Mr Hadland said.
"Any mass wildlife deaths, particularly in waterfowl like this, is a big concern — mainly because we don't know how far this might go before it's controlled.
"So I think everybody's on alert, and we should continue to be so, because it's avian botulism this time, but next time it could be something more sinister."
A Biosecurity New Zealand spokesman said it took a supporting role to manage potential exotic (introduced) diseases.
"As testing has ruled out exotic diseases being the cause, we have no direct role. We remain in contact with DCC."
Avian botulism is caused when waterfowl eat the toxin produced by the Clostridium botulinum bacteria.
The avian botulism type-C strain identified poses minimal risk to the health of humans.
