The Mucus Marshes were a treacherous and foreboding landscape located north of the submerged city of Atla. The marshes were characterized by their thick and viscous mucus, which was secreted by various seagoing creatures such as octopi and sea anemones. The mucus made it difficult for travelers to navigate the marshes, often resulting in getting stuck or lost. The area was known to be home to dangerous predators such as Wyrms and hunter sharks, which preyed on those who wandered into their hunting grounds. The notorious Sea Hag, Unknown, was also known to reside within the Mucus Marshes, using her powers to lure unwary travelers to their doom. Despite its dangers, the Mucus Marshes held great value to alchemists and apothecaries who harvested the mucus for its various medicinal properties.