There are houseboats just upriver from there, and some of the owners will dump their toilet tank right into the river. The bank just downstream of some of them smells like sewage when you go past.
I live on the bayou that connects to the Ouachita River. That's no where close to the biggest creature swimming in this area. Check this out, killed by bow in Bayou Desiard (not far from the Ouachita River.) http://www.flickr.com/photos/jacquie_wingate/3576607263/