Well here goes my horror story...
I took my 1.5 year old ruby swimming this last Friday. I took the day off from work and went in the morning to a nearby lake that I knew would be mostly deserted because it was a weekday. We played fetch in the water for awhile with his bumper - no one in sight.
Then a huge black lab runs out of the woods behind me as my ruby is going after the bumper. The lab proceeds to swim OVER my dog!
I could see my boy got hit pretty hard and was submerged completely in muddy lake water. Luckily he was wearing a life jacket and popped right back up to the surface where I was able to grab him. He was dazed when I pulled him out, I don't know if he would have been able to pull himself up.
The labs owner came running after him. The lab was dragging a leash he pulled through the owners hands as she was getting him out of the car. She apologized a thousand times, but it was just an accident - he wanted to go swimming too!
Moral of the story - if you dog is going to swim BUY A LIFE JACKET