No, they are at the water parks year round. Just below certain temps, there will be significantly fewer. And on really cold days, you won't find them there. Which is usually the day the park closes anyways.
We have a fairy one. DD loves to play with it. I like the idea of a card on a wristband. It is easier to keep up with, but we always make sure to take a picture of any photopass card we get with our camera just in case they get lost!