When I was a teenager, I was half ruptured and three-quarters drowned by a very large girl who jumped in at the shallow end without looking first! She didn't notice that I was swimming around underwater, picking up coins from the bottom of the pool. (I used to chuck a handful in and see if I had could hold my breath long enough to retrieve them all. A kind of cut-down, underwater version of orienteering!)
I got a foot in the 'nads and the air crushed out of me, and then she kind of just sat there on my chest pinning me to the bottom of the pool! I somehow summoned the strength to push her off and claw my way to the surface but it was a pretty unpleasant experience which put me off swimming at busy times.
Years later, I started going after work to Coventry's 50 metre pool. They used to have oneor two lanes for the club swimmers, another for ordinary swimmers like me, and the rest of the pool free for kids to play about in. That was okay except for the fact that I was constantly being rammed by faster swimmers doing the crawl who would never look up to see if anyone was ahead of them. We could have done with a 3rd lane for the non-crawlers.