Is it legal to swim fully clothed?

The short answer is - its illegal to swim fully clothed in every state. If you are at a public beach and try to go in for a swim in a business suit for no good reason, you are creating a public nuisance and will be stopped - probably arrested. From there on you can sue for wrongful arrest but most circuit court judges will eat you alive. There are always local laws (usually city codes or county ordinances) that prevent someone from doing something 'silly' like blowing bubbles with your mustache on Sundays. Heres the bottom line. If its your property and you want to swim in your pool fully clothed - there is practically no chance of it being illegal anywhere in the US. BUT acting strange in public is up to a police officer to make a judgment call about.