The Foulweed Fens are a series of salt marshes that border the southern edge of the Lake of Lost Memory. The salt was washed into the area by rivers from the mountains flowing into the salt waters that had been let in by the Lake’s destructive creation. The salt fens completely surrounded and undermined the garrison fort at Hallowiir’s Watch, causing sections of it to topple. This allowed the goblins of Gristamere to attack and destroy the garrison there during the Second Witching War. The goblins might’ve continued further into Summerlund, but they were driven back at the Battle of Seowyn’s Crossing.