By far the most common and tragic event is when a child drowns.  You can read the facts:

I learned to swim at an early age...I mean I grew up on an island going to the beach or a pool everyday in the summer.  I signed my son up for a swimming course at the JCC; the course was not that great and they soon replaced the instructor and improved it a lot.  However I did learn via youtube and from others how to teach my son to kick and to push off the wall with his feet.  One of the scariest moves was taking him by the chin and just moving his head while his feet and stomach rise and directing him by his head on his back.  The techniques worked and through repetition and practicing (with a noodle) every other weekend my son was able to swim on his own. The experience gave him confidence in camp being the only kid that could swim and a favorite activity for both of us.  Because of the importance of safety most community centers offer very cheap lessons and afterward you continue practicing with your child for an hour a weekend, you both get exercise and have fun.