Going for a summer's dip at the beach was a real pain for some people this past weekend.
Many swimmers were left nursing nasty red welts, inflicted by swarms of bluebottles that washed up on beaches up and down the NSW coast.
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Beachgoers reported painful encounters all along the Sydney coast from Palm Beach to Cronulla, while warning signs were erected at beaches including Bronte and North Bondi, where the sand turned an ominous shade of blue. Avalon Beach was closed due to the sheer number of bluebottles on Sunday.
And as the weather heats up to a forecast maximum of 38 degrees on Tuesday in Sydney's east and sunlovers hit the sand en masse, they've been warned that there might still be a sting in the surf.
"Looking at the numbers [of bluebottles] that were around on Sunday, even just the tide coming in and out will drag some of those back in and back out," Rob Townsend, the Life Sciences Manager at Manly SEA LIFE Sanctuary, said.
"Often when you see them in that kind of number, it does take a while for them to dissipate."
Chief Bondi lifeguard Bruce Hopkins said his team treated up to 50 people for stings at the beach on Saturday, as the south/south-easterly wind blew the bluebottles onto shore.
"We didn't have to call an ambulance for anyone, it was mainly just the welts and dealing with the pain," he said. The majority of the bluebottles at that beach had dispersed by Sunday and Monday, he said.
Mr Townsend said the float on the top of bluebottles meant they were at the mercy of the wind and the waves.
"If you look at the way the bluebottles are put together, they have that big float on the top, which kind of acts as a sail, and that's how they move around," he said.
"The float kind of leans either to the left or to the right, and so in any given wind direction, you will find that half of the bluebottles get blown towards shore, almost like the sail on the boat."
The sting a person felt upon touching the tentacle was venom, which the bluebottle usually used to catch food.
A team of scientists at the University of Sydney in 2013 examined a range of methods to treat jellyfish and bluebottle stings, and determined that hot water was the best way to treat the pain.
"Our research showed that immersing the sting in hot water was 50 per cent more effective than ice packs in relieving pain," Associate Professor Angela Webster, from the university's School of Public Health, said at the time.
"A hot shower following bluebottle stings is the best treatment for pain.
"Treating the sting with vinegar ... compared with hot water actually made the skin appear worse."
A bluebottle, which is also known as a Portuguese man-of-war, is not a single animal, but a colony of four kinds of organisms working together, Mr Townsend said.
The float is a single organism and supports the rest of the colony.
"It's a group of organisms all living together, a bit like a coral, but essentially to us it looks like one organism," he said.
Take. Care at Bondi today... lots of bluebottles!#breaking #abcsydney pic.twitter.com/D3rlGWrMLg
— Phil Rich (@FelipeRico) January 21, 2017
#bluebottles everywhere at #bondi today
— Sid Surfa Saurus (@SidSurfa) January 21, 2017