My buddy had two dogs, both young adults. A white lab, and a black lab mix from Craigslist. The white one swam like a fish. The black mutt would only go in up to his elbows, but they could not get him to swim. I was baby sitting the dogs one day and took them to a lake. I tried to encourage the black dog to swim for a couple minutes but he wouldn't. Then I pulled out the tennis ball and waved it around for 30 seconds and threw it in the lake. Whitey immediately jumped in. When the black one saw that, he ran right in and swam for the ball. He was the dominant dog and couldn't stand the thought of not getting the ball. From then on he would always swim, although he was terrible at it and never got better. He was a wierd dog. Pretty sure he had mental problems.