If the pools are heated, shouldn’t there be fog or steam rising off of them during the winter?

Many people enjoy the experience of swimming in the cooler weather, especially when there is lots of fog coming off the pool. The fog is formed when the layer of warm vapor just above the pool water’s surface rises up and mixes into cold air resulting in misty condensation.  
 
There is so much fog coming off a Hot Tub because the bubbles break at the surface allowing heat and moisture to escape and build up the vapor layer. If the bubblers/jets are not on, there is usually very little fog even though the water temperature is much hotter than a regular lap pool.

When you look at the Sports Pool and you do not see a big fog cloud, do not assume that the pool’s water is cold or the heaters are not working. The Sports Pool’s temperature is maintained as close to 80 degrees as possible all year. If no one is swimming in it, the water surface has no waves so there is not much heat or moisture escaping from the water’s surface. Once the swimmers begin swimming laps, the fog usually develops because the swimmers’ actions break up the water’s surface allowing heat to escape and vapor layer to build. 

The amount of fog you see is also affected by humidity and the wind. If there’s low humidity, you will see little or no fog, but if there is high humidity, the fog is more likely to form. Winds will blow the vapor coming off the pool away so there’s little time for the vapor to mix with the cold air to create a fog cloud.

Just as you should never judge a book by its cover, never judge a pool’s temperature by the amount of fog you see coming off of it.
 
By Erica Meyer, Aquatics Director