The Fog

The Fog is a hazardous weather condition in the Fallout 4 add-on Far Harbor. It is worshipped as a blessing of Atom by the Children of Atom and feared by the people of Far Harbor. It turned the Trappers into mad cannibals.

Characteristics
The Fog is radioactive in nature, and therefore dangerous to the residents of The Island, except for members of the Children of Atom and the synths of Acadia, who are immune to radiation. While the Fog has engulfed almost the entire island by 2287, Fog condensers created by Acadia are capable of protecting small areas from the effects of the Fog by condensing the Fog into a liquid form. The Fog, in this form, can be used to craft several useful items.

Originally, the Fog was merely an occasional presence. However, ever since the arrival of the Children of Atom, it began steadily growing until it threatened to cover the entire island. The residents of Far Harbor believed that the Children of Atom were somehow "feeding" the Fog, while the Children believe that the growth of the Fog was Atom's reward for their faith.