Any natural body of water would be a good place to practice! However, chances are that if it’s a safe place to swim, it’s open to the public just like a pool would be. If you’re practicing swimming, regardless of if you’re wearing a tail or not, you should be swimming where there are life guards present. At the very least, you should have someone with you in or just outside the water that could help in an emergency. I would check gyms with pools also. They’re slightly less public (usually because you have to be a member, but if you can afford it, it’s a good option) and other people are so focused on their workout that they don’t pay you much attention. You could always ask the life guards or pool/aquatics manger what the busiest time for pool usage is and then schedule yourself around it for a little more privacy. I hope you find a place that you’re comfortable in!