The biggest issue is poop. They don't poop just in the water, they poop everywhere. And they often eat their own poop, not just under stress conditions (as dogs do) but even when they're happy. I'm not sure if they can be conditioned, for example, to only poop in a litterbox, and to leave the poop alone.

On the other hand, thermal regulation for the water isn't that big of a deal, they're more resilient to cold than it looks like:

I think that this pic is from the same park as I posted early on. It snows once in a blue moon here, but hail is somewhat common in the winter. They handle it fine.