While many people associate webbed feet in dogs with Labrador Retrievers, this characteristic is found in other breeds, too.
All dogs have some degree of webbing between their toes, and some happen to have more than others. In some breeds, especially ones bred to spend time in the water or digging in the ground, this webbing is exaggerated and found with greater frequency. For example, Poodles, Cocker Spaniels, Newfoundlands, Dachshunds, and more sometimes have webbed toes.
Even if a dog doesn't have recent ancestry from breeds known for webbed toes, they may still have more webbing than average -- sometimes it's the luck of the draw!