Can all dogs swim?

Yes and no
Most dogs are perfectly capable of swimming. Be aware that there can be a few exceptions with the heavier, short nosed breeds. Even though a dog should be capable of swimming, does not mean he can actually swim. Some dogs panic in the water and cannot hold themselves above water with their frantic paddling. Occasionally these dogs can be acclimated to the water and learn how to swim and how to love it, some never do.
Most dogs can learn to swim and we are careful to encourage them slowly and safely. Puppies almost immediately adapt to swimming and learn to like it very quickly. Older dogs can be slightly more discerning and either love it, are neutral on the topic or simply don’t do it. Why not give your dog the opportunity to show you what category HE falls into?