The 39-year-old, who has not been named, was taking part in a two-hour session alongside two friends at Breatheolution in the Peak District.
She suddenly collapsed moments after plunging into the ice-cold River Goyt in Derbyshire on Monday afternoon.
Therapist Kevin O’Neill pulled her out of the water and gave her CPR while paramedics and an air ambulance rushed to the scene.
Despite their efforts, the woman died at the scene, leaving her husband ‘utterly devastated’.
Mr O’Neill, who runs the camp, told The Sun he was ‘reeling’ from her death. ‘I am heartbroken,’ he added.
‘I’ve not slept and I’m finding it hard to process. I cannot stop thinking about her family. It’s tragic.
‘I have taken 1,100 people into the water over two years and nothing like this has ever happened. It’s a freak incident and very sadly someone has lost their life.’
Everyone signs a waiver and is asked about their medical history and if they are taking any medication, Mr O’Neill said.
According to the Breatheolution website, the cold water therapy ‘can be tough’, including some ‘uncomfortable’ sensations on the body.
Participants have described feeling ‘euphoria that no alcohol or drug has ever given them’, followed by ‘a sense of calm’.
Coleen Rooney, wife of former Premier League star Wayne Rooney, travelled to River Goyt last year for the therapy.
Other celebrities who have visited the camp include ex-Manchester United footballer Chris Smalling and Line of Duty actor Stephen Graham.
A spokesperson for Derbyshire Police confirmed the woman’s death, adding: ‘At about 4.15pm on April 25, paramedics called us to the riverside off the B0602 between Bridgemont and Furness Vale, where they were treating a woman who had been in the water.
‘The woman sadly died at the scene. A file is being prepared for the coroner.’
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