Wettermur am See is a German word used to describe a phenomenon occurring when the water temperature of a lake rises above the ambient air temperature, causing evaporation to form a layer of fog over the water’s surface.
This is most common during early mornings or evenings in late summer or early autumn. The fog can be quite dense, reducing visibility on the lake and surrounding areas. The phenomenon is not unique to any particular lake, but it is most commonly observed in areas with calm winds and clear skies.