I do not recall wether or not the water was warm or not. I remember the air was always about 45 degrees, and I think I went in November. It gets even hotter in the "summer."
Since this is the sea, I guess the water was not that warm. If it were a shallow lake or a pool, the water would be warm. In fact, I believe that many of the hotel pools are cooled. Otherwise, you'd have to swim in warm water, which is not very pleasant, and kinda disgusting.