Final Fantasy Infinite
Conal Curach is a poisoned, desolate swamp on the Northern Continent. Originally a bountiful section of the continent and homeland to an offshoot of the Al Bhed that focused on technological integration via the earth, using vines and dowels instead of ropes and nails. Sadly, this place was flooded and destroyed during a massive storm that shook the continent at the end of The Crystal War due to the Espers leaving. Massive world instability struck here harder than anywhere else, causing a mass evacuation. Not everyone made it out.
Since then, the water in the area is toxic to all but monsters. Those drinking it are afflicted with a curious sickness, coughing up black and an eventual darkening of the skin. They return to full health eventually, but only with medical care and curative magics.
Rumors of a massive serpentine creature that resides in the swamp persist.