A perilous bog that surrounded the Misty Lake. Adventurers crossing the marsh were plagued with quicksand, giant fish, boiling waters, enchanted birds, and an occasional heart-stopping shriek.
The marsh was the home of Sir Dodinel the Wild and the wizard Malduc. Arthur’s envoys had to travel through the Shrieking Marsh to find Malduc and enlist his assistance in the rescue of Guinevere from an abductor.
Source
Lanzelet | Ulrich von Zatzikhoven, c. 1200