I live in eastern washington, around the same latitude as Ohio, and we've never had them survive in our pond. My mom just bought some more this year and put them in though. We tend to have really frigid winters, it usually gets down to -3 for around a week every winter, though that one week is broken up over a month or two. Our pond never freezes though, we just disconnect the waterfall and let the pump keep going in the main pond and run a trough heater in it (for livestock and such).