Testing is under way to determine what killed more than 350 birds at a nature reserve south-west of Bendigo.
More than 350 birds, mostly ducks, were found dead, and others injured and sick, between Thursday and Tuesday at Bells Swamp Nature Reserve.
Parks Victoria has taken samples for testing and will receive the results over the coming week.
The reserve will remain closed while monitoring takes place, with authorities warning people not to enter the water, or handle sick or dead birds. Authorities have also warned people to keep their pets away from the area to make sure they do not eat infected fish, birds or maggots.
Regular patrols by Parks Victoria will monitor for further evidence of sick or dead birds.
Sean Dooley, the national public affairs manager at Birdlife Australia, believes the most likely cause of the event would be avian botulism, a disease caused by bacteria in soil and water. Initial evidence showed no sign of human involvement and allayed fears the birds had been illegally shot.
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Avian botulism is a serious neuromuscular illness, causing problems with muscle paralysis which can result in death.
Botulism outbreaks are common during drought when wetlands evaporate rapidly, causing more birds to be concentrated in smaller areas of warmer, shallow water, and resulting in a concentration of bird faeces, Dooley said.
“I assume what’s happening [in Bells Swamp] is that it’s filled during those rains that we had in October and perhaps now, in the hotter weather, when you get big numbers of water birds with no flush of new water to refresh things, it just becomes a petri dish,” Dooley said.
“Like everyone else, we’re just waiting to see if the toxicology tests come up with anything.”
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Parks Victoria district manager Suzanne Hughes said an incident controller had been appointed to manage the response.
Personnel including staff, vets and volunteers from Parks Victoria, Wildlife Victoria, and the Department of Energy, Environment and Climate Action as well as other groups were on site Wednesday.
“We appreciate the support and concern of community members, but no further volunteers are required at this stage and we’re asking that people stay away from the reserve until further notice,” Hughes said.
“It is important that disturbance to the birds is limited, and all activities are managed to ensure animal welfare and responder safety.
“Do not enter the water, do not handle sick or dead birds without authorisation, and take care that pets are kept away from the area.”