"These guys clearly love red meat, they are devouring this", he said.
Dr Walker-Smith told Fairfax he believed the bleeding wouldn't stop because of the anti-coagulant being released by the fleas to stop the blood from clotting, in the same way leeches behave.
"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.
After three days bedridden at Dandenong Hospital, Sam on Tuesday needed the help of a wheelchair to get home, his feet still bandaged.
According to reports, Sam's father Jarrod Kanizay said while his son was recovering in hospital, his family is still waiting for a response from doctors who are still examining the weird creature.
"I walked out and saw what I thought was sand covering my calf and shook it off, and by the time I'd walked across the sand ..."
Prof Reina said the attack should not alarm people or deter them from swimming. He threw raw meat into the water and much o his dismay; he noticed hundreds of mites about 2 mm long.
The family knew of four other cases where people walked out of the water with unexplained bloody bites but Mr Kanizay said Sam's experience wouldn't deter them from going for a dip.
"You'll probably find them floating in your drink at night....and then they end up drowning in your cup", he said. Walker-Smith suggested some sea fleas might inject an anticoagulant into their food to prevent blood clotting.
"It looked really bad in the photo, his feet looked like they went through a mincer, but it's a superficial injury and more like a graze than anything else".
'He must have been very, very cold and he wouldn't have felt it'. The only issue with that theory is that sea lice leave rashes rather than bleeding wounds.
They discovered thousands of tiny bites on the teen's legs, nearly as if he had been pricked with a pin repeatedly.
Mr Kanizay added: "He's in great spirits, extremely positive and pretty amazed at how the story has spread around the world, I think the attention has distracted him from it".
Last month, a Florida man made headlines for surviving without loss of limbs from a fatal flesh-eating bacteria infection he got while hiking Mount Garfield in New Hampshire. The organization's marine biologist Genefor Walker-Smith examined samples captured by Kanizay and concluded that the likely culprits were "lysianassid amphipods, a type of scavenging crustacean".