Wellington Water is responding to an outbreak of avian botulism affecting birdlife at the oxidation pond next to the Greytown Wastewater Treatment Plant.

A number of dead and sick waterfowl have been found on the pond, and expert advice from Biosecurity New Zealand indicates the likely cause is avian botulism.

The risk to the public is low. However, people should follow the offical advice:

• Avoid handling sick or dead birds. It can make dogs and cats, as well as other domestic pets, very sick so keep them away from dead animals if you come across them.
• If you see three or more sick or dead wild birds in a group, report it to the Biosecurity New Zealand exotic pests and disease hotline on 0800 80 99 66.

The Greytown Wastewater Treatment process is not affected. The issue is limited to the oxidation pond, which is separate from the drinking water and wastewater networks.

Greater Wellington Regional Council (GWRC) has also been notified. There have also been reports of similar bird deaths at the Masterton oxidation ponds, but Carterton District Council has confirmed that its recent cases are not related to avian botulism.

Avian botulism is a naturally occurring toxin produced under warm, low‑oxygen conditions in shallow water bodies. It is not the same as Highly Pathogenic Avian Influenza (Bird Flu), which Biosecurity New Zealand has advised is not suspected in this case.

Wellington Water is arranging for a local contractor experienced in wildlife and environmental management to remove dead and affected birds from the site. This work helps prevent further spread of the toxin within the bird population.

About avian botulism

Avian botulism is a disease that causes paralysis in birds and often kills them. The disease is caused by Clostridium botulinum, a bacteria that’s around in the environment all year round. When low water levels, low oxygen levels in ponds and waterways, poor water quality/pollution and warm temperatures combine, the bacteria can quickly reach toxic levels.

Birds contract avian botulism when they eat maggots that have fed on the bacteria. Freshwater fish and eels can also be poisoned when the bacteria reach toxic levels.

A severe outbreak of avian botulism can kill hundreds of birds, eels and fish. The outbreak usually declines once cooler weather and rainfall arrives.

How it spreads

Avian botulism is spread through maggots which contain the pathogen. Birds don’t spread the disease to one another while they are alive, but if they die with the infection, other birds can contract botulism through maggots from the dead birds. Waterfowl are particularly susceptible, because the bacteria is often found around ponds and waterways. This is often where an outbreak begins.

Risks

There seems to be a low risk to human health from avian botulism, but it can make dogs and cats, as well as other domestic pets, very sick.

Don’t:

• let your pets eat dead fish, eels or birds
• handle dead fish or waterfowl with bare hands – always wear gloves
• harvest or eat birds, eels or fish from areas where botulism is present.

What we’re doing

When there’s an outbreak, we work to contain it by:

• removing dead animals from Council-owned land, to break the maggot cycle and slow the spread
• working with other agencies and organisations including Wellington Water and Greater Wellington Regional Council in combating the outbreak.

What you can do

• Avoid feeding ducks – it’s better to allow them to forage naturally.
• Don’t feed them bread – when it rots in the ponds it promotes the growth of botulism bacteria.
• Pick up your pet’s waste and dispose of it properly.

In an outbreak, you can help us contain the spread:

• If you have wetlands on your property and you find dead birds or other animals on or around the water, remove the carcasses and bury them about 70 centimetres deep.
• Always wear gloves when handling the dead animals, and wash your hands with soapy water afterwards.
• Let friends and whānau know how they can help reduce avian botulism.