Underwater dogs: Man's best friend as never seen before

They may be noble descendants of wolves, carefully bred over hundreds of years for their loyalty, companionship and abilities to hunt, point and retrieve. But some dogs just want to play catch. Again and again. Never mind if you put a body of water in the way – these hounds will jump right in. And the result, from the point of view of the ball, can be quite alarming.

This was the discovery made by the American photographer Seth Casteel during a routine shoot with a King Charles spaniel. For, despite the well-rehearsed mantra about working with animals, Casteel is a professional pet portrait artist, specialising in dogs. Since 2007 he has become much in demand among owners who want something permanent to remember their loved ones by.

"This spaniel couldn't stay out of the pool," he recalls. "He'd knock the ball in and jump after it, over and over. So I left the shoot and went to buy an underwater camera. I didn't know what the results would be like, but once I saw them, that was the start of my project, 'Underwater Dogs'."

While Casteel's portrait work is all about bringing out the best in his subjects, his snaps of dogs underwater are about exploring the unknown. "You never know what the results will be," he says. "Will the dog look silly or will it look primal? It's hard to say. I've seen some of the silliest dogs on land look terrifying underwater, and some really serious dogs on land look hysterical underwater."

Over two years, Casteel photographed more than 300 dogs, holding shoots in cities across America. "I would photograph 15 or 20 in an afternoon," he says. "It was like a model search." The best 80 images have now been selected and compiled into a book, published this week.

All the shots except one were taken in swimming pools, and required hours of patient play. "It's all about playing fetch," he says. "It was just like being at the park, except at a swimming pool." Didn't the water get pretty filthy, having 20 dogs in the pool? "Yeah, the pool gets quite dirty!" he laughs. "It starts off clear, and it's important to have crystal-clear water to capture these photographs. But once you have dog hair and dirt particles in the water, it compromises the moment. Especially when you use flash."

Casteel wears 8kg on a weight belt to help him stay below the water, and a water-resistant housing to protect his Canon camera, which he fits with a fish-eye lens. He wears goggles and a wetsuit, as he often spends a lot of time getting in and out of the water. "It also helps me avoid getting scratched," he says. "A lot of the dogs scratch me, not on purpose, but often because they want to give me a hug. They get excited to be in the pool!"

Needless to say, Casteel, 31, is a big doggy lover. "I am a dog person, absolutely. I connect with dogs. They inspire me, especially the fact that they live in the moment. If I could be a dog, I probably would be." Really? What breed? "I would be an Afghan hound. They're so interesting and mysterious."

He currently has two dogs of his own: Nola, a small labradoodle bitch, and Fritz, a Norfolk terrier. It's surprising he hasn't got more, given that he also works with abandoned dogs: he runs a non-profit organisation called Second Chance, with which he tours animal shelters worldwide, teaching staff and volunteers how to take better pictures of pets to increase adoption rates. "I have a friend who has 60 cats! I think that's a little too many. Two dogs are enough for me. I travel a lot" – though based on the West Coast, he travels 25 days in every month – "and I want to be fair. You have to know your limitations."

Ironically, neither of his own dogs has any interest in water. "They don't want to go swimming! I wish they could be in the book. I tried. I even bought a little mini pool but they're just not interested."

One of his favourite pictures is of Coraline, an Old English bulldog (see gallery above). "It's quite abstract: she looks like some prehistoric sea creature." She certainly doesn't look like a wolf, which, as Casteel says, is the common ancestor of all dogs.

"Over the course of several thousand years, dogs have become what they are today. They appreciate the luxuries of human companionship and slipping into bed with us, and of eating the best food. But they also appreciate the chance to exploit their wild instincts, and the water gives them that opportunity. And that's what these photos show: dogs going back to being wild again. And they love it."

'Underwater Dogs' (Headline, £14.99) is out on Thursday