Just because pools are heated doesn't mean the heat element will always be running. It just means that the water isn't going to go below a certain temperature, which according to
DCL's website info is 75 degrees. There have been times on our December cruises when the water in the Mickey and Goofy pools was much higher than that due to the sun beating down on them while in port without a breeze to cool the air temp. Of course there isn't a need to heat the pool water if it is already warmer than the minimum allowed -- the same way the A/C doesn't turn on if it's not above a set temperature. I pointed out that they are heated to address the OP's question if they will be too cold to swim in.
As far as the water at CC, it was cold enough all four stops there in December for us that it felt as if it was burning my skin. Of course it wasn't, but it was that cold. We had booked the stingray excursion based on the reviews and pictures that showed people just past their knees in the water. Well, for whatever reason the CMs doing that excursion that day had us go out so we were chest high in the water and I am 5'5". It was too deep for any of the kids to reach the bottom. I felt numb while in the water. The kids and DHs all got back into the water at the family beach but the moms stuck to the beach.