Dogs can stay underwater pretty comfortably

This black Labrador Retriever is Sara Fitz-Gerald’s dog ‘Shep’. It gets you thinking on how long dogs comfortably can stay underwater as opposed to a human.
The ball that the dog is getting out is quite heavy, and filled with water. This particular dog does this all the time. When you see dogs doing this type of thing, the dog
usually has a lot of desire for the toy or object. It’s very rare that you would see a dog just go underwater without a specific purpose such as a toy that he loves. How do your dogs do underwater?