Skinny dipping is awesome.
On a cycling trip, you reach a beautiful lake. Curses! You haven't brought a swimsuit. How could you possibly resolve this conflict? Remember to bring one the next time? Swim in your clothes and ride back soaking wet?
Maybe consider swimming nude for a change. You might initially feel naked because what if someone can see my bum‽ True, but so what? Judging from how the rest of humanity has managed, you will be perfectly able to take a swim, possibly feel like a creature of nature, then let the warmth of the sun dry your skin.
I recently went swimming with a host family. The little kids asked me: Why are you putting on swimming togs? As an answer, I lied that people don't want to see me naked. What I couldn't explain to them was how people feel like they should mind seeing me naked, although they probably wouldn't.
Just as a portrait photo doesn't steal your face, you won't lose your bum if someone sees it.