This isn’t fog — it’s a phenomenon referred to as «sea smoke».
It’s not totally uncommon here, but I’ve never seen it as pronounced as in this picture. It was last year … a very cold morning, and I just happened to click on the link to one of our webcams. All what you see, looking as smoke or fog, is normally water in the harbour.
The camera is situated on top of the tallest building in the city, the Bell Building, which in turn sits on top of a hill. It’s fun to check it out in the morning, because you never know in which direction it will be pointed.
Sea smoke occurs when really cold air moves in, and the water is warmer than the air.
Here’s another one, I took, myself, back in 2009.