Turn Back the Fog

Turn Back the Fog is a side quest in the Fallout 4 add-on Far Harbor.

Detailed walkthrough
This quest is given by Small Bertha at Far Harbor after successfully doing the "Captain's Dance" and earning the trust of the residents of Far Harbor during the Rite of Passage quest.

Small Bertha asks you to clear out Echo Lake Lumber mill, which is towards the west side of the Island. The lumber mill is inhabited by a number of feral ghouls, including a glowing one, who will need to all be killed.

Once all enemies have been cleared the quest will update and the Sole Survivor must return to Small Bertha in Far Harbor to tell her the lumber mill is clear.

Also, the fog crazed "owner" of Echo Lake Lumber, Malcolm, will show up once the area has been cleared and the player will have 3 choices: Refuse to settle the land, take the caps he offers for sending settlers, or refuse to take part in the deal (he becomes hostile).

Bertha then leads you through Far Harbor to Teddy Wright and Captain Avery who are having an argument in Teddy's clinic. Through dialogue the player will help Bertha to convince Avery to provide fog condensers to make Echo Lake Lumber habitable. This completes the quest and a few settlers will be at the lumber mill next time you arrive and you will have access to the workshop there.

Bugs

 * The quest may not update even after all the ghouls are killed. It is suggested to use V.A.T.S. to find ghouls hidden in piles.
 * When DiMA's secret of killing Avery is revealed, and you make the choice that Allen Lee keeps Captain Avery alive, but chases her away from Far Harbor never to return, Small Bertha will actually run to Teddy, but the captain won't be there, talking to Small Bertha will result in her only saying: "Excuse me, ma'am." And the quest cannot be completed by any means.