The supermodel is currently holidaying in the South of France with her husband Jamie Hince and a group of pals and was keen to get her formal qualification in diving while she`s there but her fear of sea-dwelling creatures put an end to that.
A source told the Daily Mirror newspaper: "Kate has been snorkelling before and dived a bit. She was keen to get a formal qualification, did some of the classroom-based stuff and was really getting in to it. But then she got convinced she was going to bump into a giant, scary fish - possibly a shark - and began to get nervous.
"When a school of tropical fish swam past, Kate got a bit terrified by one of the bigger, grey ones, Pals were calling her `SkateMoss` all afternoon, joking she`d stumbled across a giant skate."
So instead of going under water, Kate intends to spend the rest of her break on British businessman Sir Philip Green`s luxury yacht by relaxing with pals while sipping champagne in the sun.
The source added: "Obviously the yacht she`s staying on is filled with vodka and champagne, and the gang like nothing more than sunbathing on deck with a chilled beer or a glass of bubbly."