How do you get a young dog to swim?

The last couple of weeks I have been trying to get Buddy to swim. Josh and Eric had taken him sailing and dumped him in the water and according to the book, that is not what you should be doing. So I was afraid Buddy had gotten scared of swimming. So I took some dog treats and took him in the water and give him treats to go in deeper. But no matter what he would not go further then were he could still stand. He would even start to shiver if I kept the treat too far away from him, like he was really scarred. Last weekend it was really hot and we were all outside at the water front, so buddy would walk through the water as well. Now in that last week we had gotten company of 4 swans in the lake. And on this last Sunday they came pretty close to the house and Buddy got all worked up and excited about. He was barking at them and running back and forth in the water, and suddenly he was swimming. But then he swam back again, went in the water again and then, he just started swimming after them. The swans swam away and Buddy kept on swimming and swimming and I just went after him. He swam further and further and halfway across the lake the swans apparently had enough of this crazy dog and flew away to the next lake over. And there was Buddy in the middle of the lake not knowing what to do and where to go. I called Jenna who was kayaking and I tried to get buddy and take him to the closest shore. Rick and Eric had already taken the rowboat out and were on their way over. Buddy was pretty tired and I held on to the Kayak with buddy in my arms. When the rowboat arrived we put him in the boat and took him back to the house. And there he was sitting in the front of the boat all proud looking and still trying to see where those darn swans had gone off to!