The nights are drawing in; it is chilly and damp. But these are ideal conditions, it seems, for the country’s newly converted army of outdoor swimming fans. In the summer, the pandemic closed indoor swimming pools across the UK – about one in five have yet to reopen – and thousands of swimmers started taking regular dips in open-air pools, lakes and rivers as an alternative. At one point, demand was so high that the Outdoor Swimming Society was forced to take down its map of wild swimming spots in an attempt to prevent overcrowding. But colder weather, more challenging water temperatures and the discomfort of wriggling into dry clothing in public is failing to deter many of the converts. The National Open Water Coaching Association (Nowca), which operates bookings for 30 open-water venues in England and Scotland, from Manley Mere in Cheshire and Portobello Beach in Edinburgh to London Royal Docks, said the number of swimmers in October was up fourfold or 323% year on year, after a 60% rise in swimmers over the summer. Better, which manages leisure services for local councils around the country, said it was keeping its West Reservoir venue in east London open for swimming into the winter for the first time this year because of the high demand. The number of swimmers attending West Reservoir has soared from 1,600 in 2019 to 19,000 this year, making it busier than some of the heated pools on Better’s roster. Visits to the group’s outdoor lidos are also up despite limitations on visitor numbers to facilitate social distancing. At the popular London Fields heated lido in north London, numbers were up nearly 25% between August and October as swimmers have kept ploughing up and down the lanes in the cooler weather. Andrew Clark, at Better’s parent company GLL, said people were desperate to get their swimming costumes back on once lockdown ended because “it is not an activity you can re-create with a virtual class like Jo Wicks. The prolonged closure of indoor pools forced people to try outdoor swimming. That’s created people who have said, ‘This is me now’ [and they have carried on into the autumn].” He said the obvious health benefits had combined with a trend in exercise for “more experiences and something to brag about” by swimming outdoors in the cold. Swim England says the health benefits include better sleep, circulation and increased happiness. A report published last week suggested that outdoor swimming could even delay dementia. South London swimming club (SLSC), which manages winter swimming at the unheated Tooting Bec Lido, said more than 330 additional members had signed up this year, with double the number of people swimming daily in October compared with last year – despite the pool temperature now dropping to about 11C (52F). Margy Sullivan, SLSC’s membership secretary, said more under 45-year-olds had signed up than usual: “It’s a much younger demographic. Outdoor swimming became the thing in the summer when pools were closed and a lot of people took to the sea and rivers and lakes. People discovered they could swim outside.” She said the switch to working from home had made it easier for locals to pop in for a morning or lunchtime swim, while the younger generation had committed to the sport by buying the latest kit, such as changing robes and gloves. The surge in outdoor swimming has been a boon for kit suppliers. Sales of swimsuits are down because of the closure of indoor pools, but cold water gear is thriving. Frostfire, which makes the Moonwrap waterproof changing robe, said sales were nearly three times those of last year and its factory has been working at maximum capacity as demand continues into the autumn. The online sports retailer Wiggle said demand for wetsuits was up by 80%, and sales of accessories such as neoprene socks, caps, and gloves – vital for many open-water swimmers to keep fingers and toes warm – are up by more than 150%. However, not all outdoor swimmers are looking to chill out. At Hathersage pool in the Peak District, where the water is heated to 28C in October, the number of swimmers taking a dip this month is nearly three times that of last year, and there has been a surge of almost 90% since July, despite social distancing limitations. George Foy, the pool’s assistant manager, said: “People want to be outdoors. In this Covid situation, all the advice points to being outdoors as much as possible, and once people have been here, they see how they can swim into October.”