Asked by: Maggie Stills, Colchester
Basic principles suggest that the answer is 'very close' - within maybe tens of metres - so long as you are totally immersed in the water when the lightning strikes. The electric current has to pass through your body to do you any harm, and the conducting sea water will carry a good deal of the current around your body. You are at much greater risk if you are protruding above the water in a boat or on a windsurf board, as I once was during a lightning storm in Australia. My answer was to get into the water and stay there - sharks notwithstanding.
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