Sam Kanizay, 16, felt sore after football on Saturday and decided to soak his legs at Dendy Street Beach in Brighton. Half-an-hour later, he walked out covered in blood.
"I didn't really know what to think of it. It was a bit of a shock and a bit of a random thing to see, I wasn't expecting it at all," he told ABC News.
"No-one's seen anything like it or anything before."
His family believe microscopic sea lice were eating the flesh on his legs, but no-one's really sure what caused the damage.
"When he got out, he described having sand on his legs, so he went back in the water," his dad Jarrod Kanizay told AAP.
"He went back to his shoes and what he found was blood on his legs.
"They ate through Sam's skin and made it bleed profusely."
Sam said when the blood was washed off it was easier to see the holes.
"It took a while to get all the blood off and it came back pretty quickly," he told 3AW on Monday.
"It sort of looked like hundreds of little pin holes, or pin type bites, distributed all over my ankle and the top of my foot."
They couldn't stem the bleeding and went to hospital, where staff were at a loss to explain what had happened.
"As soon as we wiped them (his legs) down, they kept bleeding," Mr Kanizay said.
"There was a massive pool of blood on the floor (at the hospital).
"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)."
The next night, 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.
Sam is still in Sandringham hospital, but is off antibiotics.
"I was hoping to get out of here today but I might have to go to the specialist," he said.
"So it has been interesting. But everyone's been really supportive and everything, which has been great."
"I would hate to see anyone else going through this, obviously, it was a big shock. There was a lot of blood, who knows what is going to happen going forward. And, yeah, if we can prevent it for anyone else, that is the aim of us talking to people," said Sam's mother Jane Kazinay to ABC News.
