I know what you're thinking (not trying to be stereotypical here, but this is what I hear) - "That's so boring." "You're just working out with the old ladies." "How can that really be a challenging workout?"
Well, how do you know unless you've tried?
Absolutely, water aerobics may not have the animal impact or outdoors drive associated with a hard run or bike ride outdoors. But if you are recovering from injury, it's a great alternative. And if you're sore from a series of challenging, hard workouts; then water aerobics is the best way to maintain cardivascular stability while giving your muscles a break!
You don't burn as many calories with water aerobics as you would a run, but the benefits are still extremely beneficial.
Here are some links to a variety of posts that show the benefits of water aerobics --
And again, if you have access to an indoor pool, this is a great off-season exercise. You NEED to give it a shot!