So you’re an innovative photographer who’s hit it big taking shots of dogs looking amazingly cute underwater. The images feature wide-eyed aquatic canines — English bulldogs, Dachshunds, Boston terriers — paddling after tennis balls open-mouthed in a cloud of shiny bubbles. Our best friend at play as you’ve rarely see him. The photographer is Seth Casteel, and he created a dog tsunami online a few years ago when his photos went viral. Appearances on television followed, and then came a 2012 book, “Underwater Dogs,” which shot up the bestseller list and became an easy choice for gift-givers.

So, how do you follow a smash like “Underwater Dogs”?

Well, “Underwater Puppies,” of course. Casteel’s newest contribution, coming in September, has puppy Beagles and labrador retrievers and border collies underwater looking somewhat more floppy and goofy than their older counterparts, and just as cute, if not more so.

But puppies?! The man threw puppies into the water!? Not to worry. “Puppies already know how to swim even at just a few weeks old,” Casteel writes in a brief introduction. The pups in the book are between six weeks and six months old, and each one got swimming lessons to prepare him for his close-up. And once they get the hang of it, the young pooches can’t seem to get enough: they start jumping in on their own.