Due to some unknown property, these marshes calcify animals who die there, like Lake Natron in Tanzania. The water is incredibly unhealthy to drink, and even spells like Purify Food and Drink will not last as long as they might normally do. (Water with that spell cast upon it lasts 24 hours before being corrupted in the open air. Sealed containers preserve the cleansing effects of the spell.) Consequently, any group traveling through Ghostmire without a cleric or druid to cast the spell is never heard from again.