Bombs away; "just toss'm in, they know how to swim." Many people figure that dogs are natural born swimmers; but that is not always the case and how you approach swimming and the water can make or break a great swimmer. I remember an incident years and years ago; a guy who had just added an adorable 6 week old Airedale puppy to his family tossed her off a raft. She immediately sunk and then came up splashing and panicking. He had to eventually scoop her up to save her and when she got her paws on the sand she ran for the hills. I can't say that I blame her; what an idiotic thing to do, honestly.
Most dogs of course can swim; but many need help. They are by far much better than us at adapting quickly but if they are not introduced to swimming at a young age and in a gentle manner; things can go very wrong. I have made numerous attempts at teaching Luke to swim; not an easy task. He is a very nervous type so he tightens up and stresses. Unfortunately we don't have a lake here to practice in; we only have the southern California coast which has fairly big and ominous waves. These waves will pick you up and toss you upside down so teaching a dog to swim in them is out of the question; unless they are fearless, a lab or golden.
I've seen many dogs charge into the water without ever being in it before. They dive in head first; spit and sputter and eventually get it. while nearly drowning in the process. But they find their way and become official water dogs. But for a great majority of dogs; they need our assistance, water can be very confusing. Walking in the water is great; lots of dogs love it. But take the ground away and they panic; they reach down hoping to catch a toe on a piece of ground beneath them. As they reach further and further down they become vertical; not a great position to swim in. Then comes the frantic splashing; of course they will panic, they're sinking.
Turns out that I eventually ended up with that Airedale who was tossed into the water at 6 weeks of age. And I had to teach her to swim; being an Airedale she was a natural water dog but had no idea how to swim. She never found her way on her own and would simply sink as she was reaching for the ground. You must take great care when you are around any dog in the water; even the best of swimmers will try to use you as a floatation device at times and you can get injured as they attempt to climb you. So; in water deep enough to swim in you must hold up their rear end; it is not an easy task. With my Airedale gal I simply held her tail; she was very buoyant so this was all it took to keep her afloat. Their legs are naturally swimming so once they start to propel themselves; they pretty much take over. The trick is to create a calm atmosphere; otherwise they cannot even think. Mandy (the Airedale) actually turned into one of the most amazing swimmers I've ever met. She would go into the water and come back in an hour; she loved it and would dive deep under the water to pull out boulder sized rocks, she was an amazing dog.
Other dogs need a bit more; a lift from beneath, something to stop them from sinking in the rear. Often just barely holding them under the chest and lightly moving them about to get them moving on their own. Many people use life vests for dogs. This of course is a great thing to use when on boats with your dog and a must for many of the shorter legged dogs. But using it to teach swimming can be both good and bad. If you use it for just the introduction it may be good; a few days of floating and then take it off. Unfortunately many dogs will end up back at square one once you take it off. You have given them a false sense of swimming and now they think it is easy peasy when the realization "sinks" in.
Tilley had the luxury of learning to swim in lakes; she did it herself mostly. A couple of helping lifts and she was on her way. She loves to swim; dive and go under. My son and I use to get out our masks and watch Tilley go under water for her toys that had sunk to the bottom of the pool. How I wish I had an underwater camera back then. Watching her teach herself to hold her breath was amazing. Luke has done the same; albeit from the safety of land. He puts his head underwater to get his toys from his kiddie pool. It took him a couple of tries before realizing that you cannot smell the toys under the water. Watching the process of the breath holding is amazing; it is done fairly quickly. From water up the nose to whole head submersion in a matter of minutes.
Be safe around water; dogs do drown. If you have a dog that has shorter legs take extra precautions. Many cannot swim at all and simply sink. Pools are very dangerous with dogs; even the best swimmer can drown if they cannot get out of the pool. Teach your dog how to exit the pool "in case" there should ever be a need. And always supervise swimming activities.
Patience is the best line of attack for teaching your dog to swim; make it fun. Never push; pushing causes all sorts of issues; one is pushing back. The harder you push the harder your dog pushes back. You want your dog to trust you; trust is all important with dogs. And if they simply are not interested after all your fun attempts to get them into the water; maybe they'll love Frisbee, flyball, agility or going for a bike ride.