"The water is obviously icy cold and people can die of hypothermia very quickly or drown if they are caught under the ice, " he said.

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Crabs and other marine invertebrates die when the water is too cold, because they cannot flush magnesium out of their systems.

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Deaths associated with immersion in cold water have been attributed to hypothermia, since many of those who die are judged to be competent swimmers.

BBC: Cold water increases drowning risk