A Melbourne teenager has gone for a dip at the beach and come out covered in blood and looking like a horror movie extra.

When Sam Kanizay, 16, felt sore after football on Saturday, he decided to soak his legs at Dendy Street Beach in suburban Brighton.

Half an hour later, he walked out covered in what his family said were tiny marine creatures eating his legs.

“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.”

Mr Kanizay couldn’t stop his son’s legs bleeding and they 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,” he said.

Sam Kanizay’s legs were left a bloody mess after a suburban soak. Photo: AAP

“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).”

Sam was given painkillers and antibiotics and had blood tests.

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.

Mr Kanizay told Fairfax media his son’s legs were still seeping blood on Sunday afternoon. He is expected to make a full recovery.

– AAP