As one of the world's most talented and skilled surfers, you'd think the potential dangers of the ocean wouldn't be a concern for Marks. Well, you'd be wrong. She told Reuters that drowning is one of her biggest fears, but given that navigating those risks is part of the job, she's working on it. "You realise how long you can hold your breath and it's longer than you think," she said, regarding the breathing exercises she's been using to help conquer her fears.