Post Greyhawk Wars: 585 CY
The Hool River’s meanderings along the level terrain separating the Yeomanry and the Sea Princes’ lands are surrounded by quaking mires and almost bottomless pools. The marshes are full of natural hazards; a man can slip or fall to a watery, choking death in a few seconds. Only truly desperate human or humanoid renegades flee here, and the lizard men of the marsh are happy to eat them when they do. Lizard kings are said to have turned most of those reptilians to evil.
The Hool Marshes have their fair share of monsters. In the central marsh, northwest of Westkeep, there is said to be a community of yuan-ti with considerable magical powers who dwell within a temple which is itself magical. No reliable reports of this exist, however.