WARNING, GRAPHIC CONTENT: A Melbourne teenager has gone for a dip at the beach and come out covered in blood, 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 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 said.

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Sam Kanizay has suffered mystery injuries after dipping his feet into sea water. Photos: 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.

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Mr Kanizay couldn't stop his son's legs bleeding and they went to hospital. Photo: 7 News/ AAP

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The teenager's father said hospital staff have no idea what the tiny sea creatures are. Photo: 7 News

"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)."

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