However City of Belmont staff will continue to monitor the area.
Last Wednesday, chief executive Stuart Cole said four birds survived after being taken to a wildlife carer.
‘While individual water birds suspected to be suffering from avian botulism are found every few years, the last occurrence was in 2011 and prior to this there had not been an outbreak such as this since before 2005,’ he said.
A Department of Parks and Wildlife spokeswoman said it was believed excess nutrients entering the lake, either through storm waters or fertiliser enriched run off, high temperatures, and low rainfall, could encourage botulism bacteria to grow in sediment on the bottom of the lake.
She reiterated recent calls by the council for people to stop feeding the ducks.
‘Residents can help prevent outbreaks by refraining from feeding waterfowl, as uneaten bread will add to the fouling of the water,’ she said.
Local governments could also use aerators, control fresh water levels and remove decaying animal carcasses to prevent outbreaks.
Mr Cole said storm water quality monitoring was conducted at the inlet to Tomato Lake, and the councils worked with local industry and business owners to improve water management practices.
Two aerators are installed at the lake, with one operating 24 hours a day and the other 12 hours a day.
The hours are reduced from May to August when water quality issues are less prevalent.
‘Tomato Lake is a surface expression of groundwater and water levels are not artificially maintained,’ Mr Cole said.
‘The city does not apply fertiliser to the turf at Tomato Lake.’
The majority of bird deaths were pacific black ducks
Other species included eight grey teals, a hybrid black duck/mallard, five wood ducks, two australian grebes and a shell duck.