Probably not too cold for swimming. We went 12/6-12-10 last year, and were able to swim two days--temps got to low 80s. My understanding is that most of the time it is warm enough, although some times the temperature takes a dip.
We went in Dec 99 and went swimming with the air temp in the low 70's. The pools were heated though. I wouldn't want to stay all day, but it's refreshing for a dip and the kids love it. It may not be right every day, but when it is, go.
We always go around the end of November/early December, and always get swimming time in. Sometimes, we've seen people swimming at night, when I thought it was COLD. Daytime though has been, for the most part, great.
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