I do Zumba! It's lots of fun! The moves are quick, and the music is fast, but you're having so much fun, you don't even realize how much time is passing. There's a lot of choreography, but you don't have to do it perfectly. It gets easier the more you do it. Go for it!
By the way, when I first started Zumba, I was in the 260's. It's easier now, but no less fun! I think it's a great workout for anyone. Just do what you can. I still modify the "Jumping Jack" type moves. That's just too much jiggle for this body!
I've never heard of water-Zumba. That would be a blast this summer!