To determine if your dog is a natural swimmer, observe their breed characteristics and initial reactions to water. Breeds like Retrievers and Spaniels typically have a natural affinity for swimming, shown by their enthusiasm and skill in water. Introduce your dog to water in a controlled, shallow environment to gauge their comfort and ability. A dog that eagerly enters the water, paddles effectively, and seems relaxed is likely a natural swimmer. However, always supervise water activities, regardless of your dog's breed or initial confidence, to ensure safety.