Canberra resident Brett Wallensky discovered a dense carpet of bluebottles washed ashore on Barlings Beach, just south of Batemans Bay.
The motor mechanic told Storytrender that it was “the stuff nightmares are made of.”
“There must have been thousands of them beached and they were all alive and wriggling,” he said.
“If you fell in there and got that many stings all over you I can’t imagine you would survive.
“That is the only time in my life I have seen them in these quantities, I’ve never seen that many together before," he said.
Beach-goers have been warned that bluebottles - also known as Portuguese man-of-wars - could sting, even when washed ashore.
"They can even sting you after the animal itself is essentially dead," Australian Museum naturalist Martyn Robinson told ABC Radio Sydney.
Experts are quick to dispel the long-held beliefs that bluebottle stings should be treated alternately with ice-packs, urine, alcohol or vinegar.
Research from the University of Sydney found that hot water was the best treatment for bluebottle stings.
"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.
"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."
Mr Robinson adds that you should try to remove any tentacles carefully with tweezers or a gloved hand before submerging in hot water.