Our YMCA has water aerobics, and all kinds of swimming (kids, families, adults).
The water aerobics classes are almost 100% women, with a focus on range of motion. The instructor stands at the side of the pool and demonstrates the motions, and you do whatever you feel comfortable doing, at your own pace. This is in the shallow end of the pool. I like to do this as a warm-up for swimming, which immediately follows the aerobics class.
There is also a deep-water aerobics class which involves similar motions, while treading water at the same time. I've never seen any men in that class..
