A suspected outbreak of avian botulism is killing thousands of birds in Waikato.
The disease, which causes paralysis in birds, has been recorded in Matamata-Piako District, Waipa District and Waikato District this summer.
There have also unconfirmed reports of bird deaths in the Hauraki District.
About 3000 birds are estimated to have died from the disease in the Waikato region, Fish & Game gamebird manager David Klee said. Along with game ducks, the bacteria was killing black swans, grey teals and the New Zealand dabchick, among others, he said. "It's pretty indiscriminate, anything that sits on those ponds, seems to be affected." Although blood samples had not been taken, Mr Klee said the bird deaths all showed "clinical symptoms" of botulism.
Affected birds were showing signs of paralysis, they were flightless and, in the critical stage, had "lolling" and "drooping" heads.
Most outbreaks were occurring at municipal wastewater treatment plants - and in particular older, less used, oxidation ponds.
"The problem is a lot of these ponds no longer have working aerators, they're filling up with sludge at a great rate.
"Basically in summer, when these ponds get drawn down, you've got the perfect microclimate for botulism to occur."
The drought-like weather may have also played a part in the outbreaks, Mr Klee said. "In years like this, when we've got long dry spells of weather it's more likely to occur."
Te Awamutu farmer Carl Webber has had to pick up dozens of dead birds from his paddocks, which surround the Te Awamutu wastewater treatment plant, this summer.
He said outbreaks happened every year but this year had been a bad one.
"It hasn't been big, big numbers this year, but it has been consistent. The whole summer birds have been dying."
He said up to 20 or 30 carcasses could be seen floating in the pond at any one time. "The [Waipa] council has to be more proactive," he said.
The oxidation pond had been neglected and birds needed to be kept off it, he said.
More rainwater from within the catchment could also be directed into the pond, he said.
Manager of water services at Waipa District Council Lorraine Kendrick said the council was working with Fish & Game to prevent the spread of the disease. The council reported birds that were sick and dead to Fish & Game every fortnight, and dead birds were immediately retrieved and disposed of. "Anywhere there is a pond system you have the potential for this to occur. But at wastewater plants, nutrient levels are higher."
The council tried to scare birds away from the disused oxidation pond by using a zon gun, which emitted noise, and employed a "shooter" to fire blanks at the site. The council was also looking at whether the pond could be redeveloped, she said.
Mr Klee said the response of district councils has been mixed. "What we've found is that in areas where we have management plans in place with councils, we've been able to minimise outbreaks."
- Waikato Times