Botulism kills 1100 birds
More than 1100 birds have died after the "biggest" recorded outbreak of avian botulism in the Brooklands Lagoon area.
Between January 6 and 16 about 1000 birds died at the Kaiapoi Oxidation Ponds, with an average of 20 further deaths daily since then.
Council utilities and roading manager Gerard Cleary said avian botulism, which was caused by a toxin that thrived in shallow warm water, was common at wastewater treatment plant sites as they provided the perfect conditions for its growth.
"This is the biggest outbreak we have ever had," he said.
He said council contractors were regularly at the ponds removing the dead birds to limit the spread of the disease. About 80 per cent of the dead birds were paradise shellduck, 10 per cent were mallards and the remainder were a mixture of New Zealand shoveler ducks and swans.
Symptoms include varying degrees of paralysis, sagging heads, drooping wings and flightlessness.
Outbreaks typically coincide with periods of hot, dry and calm weather from December to March.
"We would expect that this will come to an end when we get some cooler weather," he said.
Because the disease could live in the ground for years, council staff would keep a close eye on the area to make sure if a breakout recurred it could be contained quickly.
About 50 birds have been killed by the same disease in Christchurch.
Christchurch City Council parks operations manager Ross Campbell said there was no major spread in avian botulism in either the Bromley Wastewater Treatment plant or the Lower Waimakariri/Brooklands areas.