Evaporation fog forms as a result of the mixing of two unsaturated air masses. Steam fog is a type of evaporation fog that appears when cold, dry air moves over warm water or warm, moist land. When some of the water evaporates into low air layers, and the warm water warms the air, the air rises, mixes with colder air, cools, and water vapor condensation occurs to form a fog. Over oceans, this form of evaporation fog is referred to as sea smoke. Examples of cold air over warm water occur over swimming pools or hot tubs, where steam fog easily forms. It is also common in the autumn, when winds and air fronts turn cool as water bodies remain warm.