From RHJunior Comics Wiki
The Dire Swamp is an artificially created wetland which serves as a barrier between The Seven Villages and the rest of the world. The outer marches of the Dire Swamp follow the same approximate border as the Mistwall, but it is quite a bit wider in places. The Gragum live in the swamp, and there are Racconan settlements along the inner borders as well.
The Dire Swamp is know to be the place where wizards' mistakes crawl off to die... or worse, to not die... In addition to bog dragons like Nessie's pet Oggy, the dire swamp is also home to mock tentacles, chooleys (otherwise known as swamp kraken, and the "tentacles" being "mocked"), and Quentyn's favorite: swamp jellies.