However, ever since the arrival of the Children of Atom, it began steadily growing until it threatened to cover the entire island.

Originally, the Fog was merely an occasional presence.

Condensed fog can then be used to craft several useful items. 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 is radioactive in nature, making it a hazard to the human residents of the Island, except for certain members of the Children of Atom and the synths of Acadia, who are immune to radiation. It is celebrated as a blessing of Atom by the Church of the Children of Atom and feared by the people of Far Harbor.

The Fog is a hazardous weather condition present on the Island in 2287.