I was on a swim team for a year in high school - we carpooled or were bussed to the local indoor pool facility (not affiliated with any one school) for practices and meets. IME experience (lived in several US locations), it's rare that any (public) K-12 school has its own pool. When I was growing up, we tended to live in neighborhoods that have community pools, paid for through HOA dues, so that's where my swimming experience comes from.
Where I currently live, in the US pacific northwest, we have an outdoor community pool with a very active swim team that allows down to 4 year olds to join (provided they know how to swim!). Lessons, however, are not regularly offered and when they are, it's during the day on a weekday so my own DD has not been able to participate. She's been learning informally from us though and she's finally showing an interest in putting at least part of her face in the water.
There are a few small indoor pool facilities in the area but of the three within a 20 mile radius, only one has not closed due to budget problems. YMCAs/YWCAs and some higher-priced gyms have pools but the annual membership can be $$$. Some of these places offer "water babies" classes for 6+ or 9+ months as well as lessons for older kids, which is nice because you're not limited to only summer for swimming.
That said, both DH and I (and our families) put a high value on being able to swim in both pools and open water, with and without snorkel gear, since it was always a big, if seasonal, part of our lives growing up. We also tend to vacation at beaches or lakes, so having the kids be comfortable around water is pretty important. I will say that although I consider myself a strong swimmer, I didn't like snorkeling for a long time (the mouth-only breathing is my issue, so I would use the mask and just hold my breath rather than use the snorkel) although I'm pretty okay with it now.