Chaynee, who's interested in marine life, said she saw the shark through binoculars off the north Cornwall coast.
"It was white on its belly and on its back it was grey. The fin was black with a ragged back edge."
"It was spitting the fish out after biting them and then going back for them, which is indicative of a Great White," said Chaynee.
Great Whites are often mistaken for Porbeagle sharks which are native to UK shores.
But experts say if the information Chaynee gave is right, it must have been the secretive Great White Shark.