Plunging into icy cold water is, for a small but hardy minority, an ideal way to start the new year or mark the festive season.

Outdoor swimming has been growing in popularity, and there's evidence that increasing numbers of people are taking the plunge in winter - and not just during holiday periods.

Enthusiasts speak of a rush of endorphins and boost to mental health - though there are risks to bear in mind too.

Some swimmers opt for wild locations, there's also demand for unheated swimming pools. And at venues like Brockwell Lido in London, the lifeguards have to be prepared to jump in at a moment's notice if swimmers get into trouble.

The BBC followed a team as they trained in 6.6C (44F) water.