It’s a Saturday at the Saltdean Lido in East Sussex and the beautifully restored Art Deco pool is packed. The weather isn’t great, but the drizzle doesn’t seem to be bothering the swimmers – not least because most of them are covered in fur.

A pointer is doing lengths, watched by a retriever with a squeaky toy in its mouth. Labradors shake themselves dry on the side and a chow skips about in the shallows, yelping with joy.

Amid it all are a few humans, paddling alongside their pets, grinning from ear to ear. Have they all gone barking mad?

‘The fact this place had just had £3 million spent on it and we’d gone and filled it with a load of dogs did make us laugh,’ says Rebecca Crook, one of the volunteers who helped save the lido, when we sit down for a chat after the soggy pawprints have dried and the pool has been drained for cleaning.

One of the original volunteers who helped save the Grade II*-listed lido from being turned into luxury flats, she took part in the swim with her two dogs: Alfie, a water-loving, 10-year-old collie cross, and seven-year-old Jack Russell Maisie (who stuck to the paddling pool).

‘The whole thing started as a fun fundraising idea,’ she explains.

‘We weren’t sure how much interest we’d get, but the first session sold out in 10 minutes.’

Not all dogs love water, but, for those that do, a body of it full of people is irresistible. (A friend who walks his dog on Hampstead Heath still winces at the memory of the time his four-legged friend ran away and hurled herself delightedly into the Ladies’ Pond; with my friend prohibited from entering to collect her, she was towelled off and fussed over in the lifeguards’ hut until a woman could be found to collect her.)

For a nation of dog-lovers who think nothing of planning our lives around our pooches, however, we’ve been slow to embrace canine swimming sessions. They were pioneered in the Netherlands, where public pools often welcome four-legged bathers on certain days and dedicated beaches are hugely popular.

Taking part in a dogs-and-owners swim isn’t merely a lovely way to bond with your animal, it can also have tangible health benefits – a 2016 study at Hartpury University Centre in Gloucestershire found that supervised swimming improved the range of motion, stride frequency and stride length of all the dogs that took part in it, even those that were already fit and healthy.

However, the type of water you choose matters. Lakes and the sea can be risky for dogs to venture into (‘you always worry that they’re going to go too far out,’ admits Miss Crook), but heavily-chlorinated pools aren’t good for them, either. Lidos are an ideal compromise: usually filled with purified fresh- or seawater, they’re kinder on eyes, fur and sensitive noses.

In Oxfordshire, the last September day of the swimming season at Chipping Norton’s handsome lido is given over entirely to doggy paddle – the boilers will have been turned off a week earlier, so the water is invitingly cool and the staff lay on balls, bowls of water and Bonios. Seventy dogs and their owners take part in what the management says was the very first swim of its kind in Britain.

‘We get a lot of retrievers and poodle crosses, but it attracts all sorts – even the occasional pug,’ says Hattie Creese, who works at the pool and borrowed Domino, her cousin’s springer spaniel, for the occasion in 2017.

She found it wasn’t only the dogs who got the chance to socialise. ‘This is a really doggy community and it’s a fantastic way to meet other owners, especially if you’re new.’

The first swim at Chipping Norton was held in 2013, and was only organised to help the manager’s German shepherd, Juno, get over her fear of water; only about three dogs turned up. Now, however, Chipping Norton Lido gets enquiries from eager humans as early as January, desperate to claim one of the spots for their pooch. And once they’re through the doors, the swimmers go gleefully wild – last year’s event was like something between an Olympic diving final and the closing scene of Grease.

A few of the participants were even fitted with special underwater body cameras to capture the fun, like furry Jacques Cousteaus.

‘It was madness,’ Miss Creese beams. ‘You’ve honestly never seen a happier group of dogs.’

Or humans, by the sounds of things.

For details of forthcoming Saltdean Lido Dog Swims and the Chipping Norton Lido Dog Swim, visit www.saltdeanlido.org and www.chippylido.co.uk