re: What age do you let kids swim unsupervised?

I started taking swimming lessons when I was 3 or 4, and by the time I was 5 or 6 I would get dropped off at the community pool with my siblings for the day, or walk/ ride our bikes there with my friends in the neighborhood. That pool had lifeguards, so I'm not sure if that falls under the category of "unsupervised", but none of our parents would be around.