Usually we get fog over lakes on calm and clear mornings. When the air is calm (little to no wind) and the sky is clear, the air directly above the water becomes saturated and fog develops.

Now on some mornings, the wind is strong enough to keep the air mixed up and this keeps the fog at bay. When the air is moving, the fog usually doesn't settle into place as easily. Also if the air is extremely dry, even the air directly above the water has a hard time becoming saturated. This is why sometimes you will see fog over lakes and other times you will not.

Keith Monday WSOC-TV Meteorologist