The following questions were answered by meteorologists Barbara McNaught Watson and Al Peterlin.
A: Bodies of water, such as lakes, ponds, and rivers, are much slower to cool down than land areas are. During clear fall nights, the warmth of the land escapes into space. As the air over the land cools, it will drift over the warmer pond. A thin layer of air above the pond is warmed by the pond water. Water evaporates from the pond's surface into this thin layer. The thin, warm, moist layer of air over the pond then mixes with the cooler air from the land. As it cools, condensation occurs and a fog forms. It looks like steam rising off the water, hence the name "steam fog." In the spring, the ponds are usually colder than the surrounding land. Just as they are slow to cool, they are also slow to warm. (Barbara McNaught Watson)
Q: Why is fog down so low?
A: Fog can be thought of as a low-down cloud hugging the ground in valleys and along rivers and streams. A cloud is nothing but fog with an "attitude" the attitude is altitude (height). A stiff wind can lift a fog away from earth, becoming a cloud, but generally fog evaporates in the morning sun. (Al Peterlin)