Is skinny dipping legal

It depends where you do it. (in the US) most places where people swim with other people, in public skinny dipping is illegal, however, if you go swimming by yourself, and no one can see you, then there is nothing wrong with skinny dipping.

In Europe adult women frequently swim topless. Some adults wear thongs or g-strings. Swimming in your birthday suit is not a big deal. it's fairly common for people to go skinny dipping.