While the motion of swimming is usually instinctive in a dog, the desire to swim might not be. It depends on the dog. Rowyn likes wading into the water, but wouldn't voluntarily go past where he could feel his feet touch. I'd tried carrying him a few feet past the step, then letting him swim back, to demonstrate he was capable of swimming. But, that didn't really convince him. It was time for stronger measures; I acquired a DFD. Doggie Flotation Device.
Rowyn still needed some gentle persuasion and encouragement, (Come on Boy, you can do this. I believe in you. I'm right here to help if you need it.) but we finally got to this;