A man riding on an inflatable tube was knocked unconscious after he flew off the float and landed in the water.

Marine Police, who have not released the man's name were called to the waters near Cambridge Beaches where they found him unresponsive in the water with his head supported.

A Police spokesperson said the injured man was lifted into the boat and taken to 9 Beaches Resort for medical treatment.

"The unresponsive male was lifted onto the police boat, put prostrate on his back. He was then transported to 9 Beaches where paramedics could have better access," the spokesperson said.

"The man was then taken to the King Edward VII Memorial Hospital."

A CAT scan was performed at the hospital before the man was said to have recovered sufficiently from his injuries to be released.