Two hundred people ran into a nine-degree sea on Sunday.

The thermometer clipped to the lifeguards’ flag on the beach at Harrow Light read nine degrees at a quarter to ten on Sunday morning. The air was not much warmer. Neither fact seemed to discourage the two hundred or so people gathered on the sand in dressing gowns, woolly hats and, in at least one case, a full lobster costume, waiting for the horn that would send them sprinting into the sea.

The first winter dip of the season, organised by the Harrow Light Shiverers swimming group, has become one of the region’s more unlikely autumn traditions. It began eight years ago with a handful of friends and a flask of tea. This year it drew swimmers from Calder, Port Selwyn, the valley and the hill towns, and raised more than £6,000 for the coastguard and the local lifeboat station.

Ten o’clock, and in

At precisely ten, the horn sounded and the crowd surged down the beach. The noise as they hit the water – a mixture of shrieks, laughter and the occasional word not fit for print – carried to the café on the promenade, where a second, warmer crowd watched with coffee in hand. Most swimmers lasted a minute or two before running back out. A smaller group, wearing bright tow floats, swam a slow loop out to the marker buoy and back, about two hundred metres, before emerging pink and grinning.

“The first ten seconds are horrible. Then your body works out what’s happening and something switches on. By the time you get out you feel like you could run up the cliff. That’s why people come back every week,” said Moira Fennimore-Hale, one of the group’s founders and its unofficial safety officer.

Mrs Fennimore-Hale, a retired paediatric nurse, briefed every swimmer before the start: no diving, no swimming alone, no staying in longer than feels right, and a warm drink immediately afterwards. Volunteer lifeguards in wetsuits stood in the shallows throughout, and a lifeboat crew waited just offshore.

From the gallery

Our photographers spent the morning on the beach, and the images capture the mood of the day: the nervous huddle before the horn, the explosion of spray as the front row hit the water, a father carrying his teenage son out of the waves on his shoulders, and the slow, steaming line of swimmers queuing at the tea urn afterwards.

The costumes, as ever, were a highlight. The lobster was joined by a family of four dressed as penguins, a group of nurses from Calder General in matching scrubs, and a man in a dinner suit who walked calmly into the sea up to his chest, adjusted his bow tie and walked out again to loud applause. The oldest swimmer, eighty-one-year-old Bernard Kilbride, has taken part in every dip since the first and said he had no plans to stop. The youngest, at eleven, was accompanied by her mother and was in and out before most of the adults had reached their knees.

Several swimmers spoke about why they had come. For some, it was the charity; others described cold water as a way of coping with stress, grief or long winters. Tamsin Okereke, who works night shifts at a care home in Port Selwyn, said she had started swimming with the group in the spring after a difficult year. “I didn’t know anyone. Now these are the people I see every Sunday. The sea is just the excuse,” she said.

A word of caution

The coastguard welcomed the event but repeated its annual warning that cold-water swimming carries real risks, particularly for people with heart conditions or who are new to it. Cold shock can cause sudden gasping and panic in the first minute, and hypothermia can set in far more quickly than swimmers expect. Anyone thinking of trying it is advised to join an organised group, enter slowly, stay close to shore and get warm and dry immediately afterwards.

The Shiverers meet every Sunday at ten throughout the winter, weather permitting, and say newcomers are welcome. The next big event is the traditional New Year’s Day dip, when the group expects even larger numbers – and, if past years are any guide, an even colder sea.