Swimming Attire

No - they wear shoes and hats etc in Sims 3 - they do not come off due to the game mechanics. I know i used to complain about it. It is still the same way. It also was the same way going to bed - if you put slippers on the sims - no matter which sims game it is - they wear it to bed. Drives me nuts. LOL.

If you want them to not have on shoes or hats - don't put them on the sim.

I saw that someone else had taken advantage of the ability to have multiple outfits of the same type and they'd design one "in the water" swimsuit and one "on land" version with hat, shoes, etc, then just change them when they were in the expropriate situation. So I've been doing the same thing, including sometimes using the "cover up" outfits as the "on land" version.

Worked for me so far.

When I swim in the river, I actually do swim with shoes on to protect my feet. It looks weird in the swimming pool, though, so only my more uptight Sims get shoes as part of their swimming outfits.

On a related note, I wish we had more variety in our swimwear options. CC seems to focus primarily on sexier styles, which don't always work for certain characters. Although it is funny to see my elderly Gene Roddenberry Sim in some of those options, lol. :D