Setting the scene. It is a chilly December morning. The temperature is hovering in the low/mid 20s. There is frost throughout a park. At the center of that park is a large pond. The temperatures are below freezing, but the water continues to maintain its fluidity because of its source: A karst spring. From that pond, there is what appears to be steam coming from that pond.
Another scene. It isn’t as cold, but the temperatures around around the freezing mark. That same pond has what appears to be steam coming from it. In addition, dense fog has covered parts of the city. Some of the fog has created ice crystals in certain places, such as a wooden bridge at the aforementioned park.
Two cold, frosty mornings, and the same foggy scenes at a pond in the park. Welcome to the steam fog. This is what happens when very cold air passes over a relatively warmer body of water. Water vapor from the pond condenses because the air temperature above the water has cooled beyond its dew point. The air is saturated with water vapor. This is what forms steam fog from ponds, lakes, and oceans. This is also known as sea smoke.
This video, is from November 2019.