On National Dog Day, those who cherish their slobbering, four-legged friends take a moment to offer their companions an extra chin rub. Those who lack a puppy of their own can resort to the next best option: the treasure trove of dog photos that is the Internet. Even decades-old archives have much to offer, including these images of a 3-year-old German shorthaired pointer named Bellybutton, who captured LIFE Magazine’s attention in 1966 with his underwater agility.
Bellybutton was unique not for his swimming abilities, but for his willingness to dive to retrieve an object. Most dogs retrieve sticks and balls from the water’s surface, but Bellybutton would go as deep as 20 ft. and remain submerged for up to 15 seconds. He even practiced his skill on his own—one day, LIFE reported, "he dived unbidden into a lake and fetched his master a 10-inch catfish.”
Liz Ronk, who edited this gallery, is the Photo Editor for LIFE.com. Follow her on Twitter @lizabethronk.