Congratulation on such an awesome loss!!
Just a quick google and I found http://www.waterworkout.com/
Back in college I was a water aerobics instructor at the local YMCA, to be honest, one of the best pieces of advice I have is really that it is just like regular aerobics... juts move in the water
For beginner classes we would just walk across teh pool, do lunges while walking across the pool, etc. For the more advanced we'd go where you can touch and do water jogging while treading water.