Bone Rot Swamp (The Blackroot Falls Supplement)
From D&D Wiki
The Bone Rot Swamp is a large forest wetland directly north of Foghaven. Widely reputed as a place of black magic and evil rituals, it is accessible only by foot, and is entirely uncharted. It is also home to the Bone Rot Swamp Village, a secret and industrious community of Lizardfolk and undead monsters.