We were visiting Cuppa's sister in Toronto this past weekend. Years ago, my industrious brother-in-law built a pond, which inlcudes water cascading over rocks. He keeps koi. I'm not sure how they manage to survive out Canadian winters, but they do.
I put fish ponds in the same category as swimming pools — they're great on other people's property. Personally, I wouldn't want the bother of upkeeping either one. An unpretentious garden is as much or more than I can handle. Speaking of which, the first daffodils are close to bloom.