The number of people taking a plunge in lidos, rivers and lochs has exploded in the past few years.
Victorians and Edwardians were keen wild-water swimmers and, in the early 1900s, there were outdoor swimming clubs all over the UK.
BBC Get Inspired went to find out why people are becoming wild about outdoor swimming again.
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If you want to take the plunge, take a look at our Get Inspired swimming guide.