Kept ours open all winter, but no swimming until last week. And even then it was only a few minutes.

Since it's right outside the back, with a view from inside through three sets of sliding glass doors, I decided to keep it nice looking through the winter. It wasn't too bad to keep clean, and chlorine demand dropped way off, so maintenance was low. When it was really cold, it stayed clear without chlorine anyway.

I drained the pumps the two or three times we had freezing weather. I still have the timers on manual, and run them an hour or two just to clean up the spring stuff falling off the trees.