Sam Kanizay was at Dendy Street Beach in Brighton where he believes he was attacked by sea lice.
He walked home, "leaving a path of blood," and his father Jarrod and 14-year-old sister Gabby took him into the shower to wash off the blood.
The flow didn’t stop, with the blood seeping from pinprick-sized holes. He was rushed to Sandringham Hospital emergency department, where he was given painkillers and antibiotics as blood tests were run.
In the early hours of Sunday morning, he was taken to Dandenong Hospital for further tests.
His legs were still seeping blood on Sunday afternoon, but doctors had no answers.
A nurse stated that it may have been sea lice, "but it was just a guess."
Nick Murray and his 13-year-old son Will began bleeding from their feet after standing in the Sandringham bay for 10 minutes, and the pair believed that sea lice were to blame.
University of Melbourne marine biologist Professor Michael Keough stated that it was a possibility: "They're scavengers who'll clean up dead fish and feed on living tissue. They're mostly less than a centimeter long, and so the bites they make are pretty small, and so that's more consistent with pinprick size marks.”
"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. Just be attracted to a little bit of blood. And if he's standing in the water and he's cold and may not notice a whole lot of little bites," he added.
Doina Canta, who swims every morning off the beach where Sam was injured, stated that it could be sting ray, as a man in her Icebergers swimming group had been stung about six months ago and bled extensively.
"It was a bit of a freak thing to happen. I'm not really sure what to think of it," Sam said on Sunday.
In an email, Jarrod Kanizay warned that "something ate Sam's legs. If you are a member of the [Brighton] Ice Bergers or running groups that ice their legs at Brighton, then you may want to repost this to warn them to not stand still in it too long..."
Jarrod said of their experience at Sandringham Hospital: "We had the emergency room full of everybody that was working there just fascinated, they were all on Google afterwards, hypothesizing as to what happened. They pretty much had 10 different hypotheses but nothing yet."
Jarrod said that he was considering leaving a bloodied piece of meat in the bay on Sunday night "to see if we can catch these things."
Sources: The Sydney Morning Herald