Rain during the day moistened the air. Clearing at night allowed cold moist air to drain to the valley bottom where by morning a fog had formed.
The fog drifts along the shore and back and forth across the Lake.
Where the fog drifts through the shoreline trees, sunlight casts crepuscular rays.
My favourite scene, however, is of the fog arching in a giant wave over an obstacle, in much the same manner as water flowing over a rock in a stream.