WARNING: GRAPHIC IMAGES
Locals have got back in the water at a Melbourne beach where a teen was left bleeding profusely from both legs, questioning the theory that sea lice might be to blame.
Sam Kanizay, 16, emerged from the water at Dendy Street Beach in Brighton, in Melbourne's southeast, on Saturday covered in what his family said were tiny marine creatures eating his legs.
Doctors later struggled to stem the bleeding from scores of what looked like tiny pink-prick bites.
His father has since posted a sickening video of the creatures - scooped out of the water with a net and believed to be sea lice - feasting on chunks of raw meat.
Local swimmer Paul Duckett said he'd never seen anything like it, despite daily swims at the same spot for the last 16 years.
"We swim there every day and we're in the water for anything from 15 to 30 minutes, and no one's ever experienced anything like this," he told Fairfax Media.
"This was a first, so that's why I query whether it's sea lice or some other creature that have caused the issue."
Sam's father Jarrod Kanizay said while his son was recovering in hospital, the family was waiting for answers. Doctors had so far been at a loss to explain what had eaten through Sam's skin.
"No one knows what the creatures are. They've called a number of people, whether it's toxicity experts or marine exerts and other medics around Melbourne at least ... (and) yep, no one (knows)," he said.
"When he got out, he described having sand on his legs, so he went back in the water.
"He went back to his shoes and what he found was blood on his legs.
"As soon as we wiped them (his legs) down, they kept bleeding," he said.
"There was a massive pool of blood on the floor (at the hospital).
University of Melbourne marine biologist Professor Michael Keough said if sea lice were the culprits, Sam might not have been able to feel them biting him because of the cold.
"They're scavengers who'll clean up dead fish and feed on living tissue," Professor Keough told Fairfax.
"It's just food for them. Especially if he's been standing around for a long time, it's the chance for more of them to come in and start biting."
The night after Sam's attack, Mr Kanizay went back to the beach with a pool net full of meat and captured the creatures he said were responsible.
"What is really clear is these little things really love meat," he said of a video, shared with AAP, showing the bugs in a tray of water devouring chunks of meat.
It's not the first time sea lice have attacked a swimmer.
In 2015 a father and son were bitten while taking a dip at Sandringham beach, in Melbourne's southeast.
Nick Murray and his son Will entered the cold water, also in the month of August.
Mr Murray told the Bayside Leader he did not feel pain initially and they only realised their feet were bleeding when they got out of the ocean.
They sustained multiple bites to their lower legs and they saw the creatures still clinging to their feet once they'd washed away the blood.
"I wonder if it was just that night, just that spot, at that particular time," Mr Murray said.
"We stood still for 10 minutes so it may not have happened if we moved about, but I wouldn't want to stand still there for a couple of hours or it may get quite bad."
Professor Keough told the Bayside Leader sea lice were an irritant.
"They are generally just a nuisance rather than a serious problem," he said.
"They have sharp jaws, so the bite is quick and a bit painful, but nothing beyond that.
"Some are active predators, and it's those and sometimes the scavenging ones that may bite."