https://www.youtube.com/watch?v=g9F_ZVTSoWw

This isn't flowing over the hill from a reservoir the other side - milder humid air is chilled as it hits the escarpment (beyond) and condenses into a more or less static fog bank over the higher areas.
Sometimes it is there for days on end in winter, when the sun hasn't enough power to warm things up - but did lift soon after noon today.

Lovely bit of time lapse, but a few seconds into the video I found myself turning the volume control right down on the PC.  

Very nice.