Eastern Australia welcomed a deluge of rain which put out bushfires and filled dams, but the wet weather could also boost mosquito numbers as the pernicious insects flock to floodwaters to breed.
NSW's latest mosquito monitoring report says "very high" numbers are concentrated in Sydney's western suburbs, including Parramatta, and in the Georges River at Bankstown and Illawong.
Large numbers were also recorded on the coast at Port Macquarie and on the Queensland border while in inland areas, populations are low.
However, recent heavy rainfall could trigger dormant mosquito eggs to hatch and swarm flooded regions.
Medical entomologist Cameron Webb, of NSW Health Pathology, says more mosquitoes are to be expected as the rain fills up wetlands and flows into bushland.
"Australia is home to dozens of different kinds of mosquitoes which either breed in salt water wetlands and briny mangroves or in fresh-water habitats, irrigated areas and bushland," Dr Webb told AAP.
The most concerning are the aedes vigilax and culex annulisrostris mosquitoes, salt and fresh-water breeders respectively, which can carry diseases such as Ross River Virus.
Only female mosquitoes bite as they need the nutrients in blood for their larvae.
But if one bites a wallaby or kangaroo infected with the virus they can transfer the illness to their next human victim.
And while it isn't fatal, Ross River can cause a fever, severe joint pain, swelling and fatigue lasting weeks or months.
Dr Webb said an increase in mosquito numbers doesn't always lead to an increase in infections.
He warned climate change could also increase mosquito numbers.
"It's difficult to predict but on balance more mosquitoes are likely as there's an extension of the season into spring and into autumn," he said.
And wiping them out isn't easy, as Dr Webb discovered when bushfires destroyed one of his mosquito monitoring stations last month.
When he visited the site a few days later he found the mosquitoes had returned.
"They moved back in very quickly so we know the eggs must have survived the fires," he said.
By lying dormant in the soil it was likely they were protected from the intense heat, he added.
"They're pretty hardy, they survive through winters and drought as eggs and as soon as those areas flood they hatch."
However the bushfires also wiped out most of the mosquitoes' food source which could have long-term affects.
"It could be that as the surviving animals move nearer to people where there's food then the mosquitoes may follow," he said, leading more opportunities for diseases to be transferred.
"We just don't know, we've never had an extreme event like this before."