Swimming for exercise
I don't do water aerobics but I do swim for just over an hour every morning. I'm training for the Ironman so swimming is part of my training schedule. I do find swimming to be MUCH less stressful on my joints than running and biking which I also do on a daily basis.
As far as swimming classes in Baton Rouge... You may want to check with the Woman's Center at the corner of Jefferson and Bluebonnet. I've seen ladies in the pool doing aerobics when I attend support group meetings there. If you are looking for structured swim training you may want to check with Crawfish Aquatics. http://www.crawfishaquatics.com/ They are in the Swaggart complex on Bluebonnet. They offer masters swim training and although I haven't been people I've talked to in the Baton Rouge Triathlon club rave about the classes.
Chad.