Dogs instinctively know how to swim. If they like swimming or not isn't quite as easy to determin. Put a little water in the pool- id's say up to his knee level at first. Try to not have the water too hot or too cold if you can. Get in the pool with your puppy and bring some treats, toys, and a fun attitude. Play with your puppy. He will let you know how to continue the "game." Don't overwhelm him, but make it a fun experience. Do this a few times and see what the reaction is. If you keep it fun, upbeat and positive, you should have a pup that loves the water. Your pup will "tell you" with his own responses how fast you should go and how deep you can make the water. COntinue to get in the pool with the pup for quite some time (for safety sake and to show it's nothing to be afraid of).
Swimming is an excellent activity for dogs, but not all dogs enjoy it. Taking this time as a pup ensures you will have better success than with an adult who's already decided not to enjoy the activity. Just take it at your pup's own pace and level of security. At any point your pup seems cared or nervous, you've gone too far too fast and you should take it back a step or two. Good luck and have fun!
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PHReign