Wild swimmers have voiced disquiet at British Triathlon over safety advice warning people not to enter waters below 11 degrees, as they claim the coldness helps improve “mental wellbeing”.

Last year, almost half a million people swam in open water venues such as lakes and lidos, with many hobbyists claiming health benefits are among the attractions to immersing themselves in chilled water.

Swimming in colder temperatures can relieve symptoms of depression and improve people’s moods, research by the British Medical Journal Case Reports has found.

The number of people regularly taking part in open water swimming rose by over 80 per cent between November 2016 and 2018, according to Sport England.

However, enthusiasts have warned the growing trend may come to a halt as a result of the initiative by British Triathlon to encourage more people to compete in the sport.