I wonder if they just weren't acclimated...kind of a shock factor, because I know most don't mind the cold. I only have a kiddie pool and they used it year round, even when I knocked ice apart so they could use if wanted. I know one time they went in and got right back out and didn't use it for quite some time for bathing one of the days I knocked the ice out. But next year if they continue using the creek daily as it got colder in the fall into winter, maybe the cold won't bother your one like it did.