What Causes the Mists above Lakes and Ponds?
The mist that may be seen above ponds and lakes on cold winter mornings and clear summer nights is sometimes called steam fog. It forms when there is a big difference between the temperature of the water and that of the air above it. During the night, the air often cools off much faster than the water.
The warm water from the surface of the lake evaporates into the cold air above. The sudden cooling of the rising water vapor changes some of the dampness into very small droplets of water, which float above the lake as steam fog. In the morning, as the sun heats the air and temperatures rise, the water vapor evaporates and dispels.
Fog is simply a concentration of low-lying water vapor in the air. In the fall, these tiny liquid water droplets often form over bodies of water like a pond or a lake. Fog forms when cool air and warm water meet and, more specifically, when the difference between the temperature and the dew point is less than 4° Fahrenheit.