The north fork of the Holston is fed by water that drains from the coal fields...there have been mercury warnings related to fishing in that river for decades. The south fork flows by Eastman....ever worked at the Big E sport? Do you realize that the Patrick Henry dam does a release early every morning to sort of push things down stream. I used to work with the gang that fed the african geese that lived on the river. I always joked that we had to wind up the geese. As far as the French Broad goes, some portion of that flows by Canton and the big paper mill. Tennesse has had several squabbles with NC of water quality and dioxin poisoning, also for decades.
The Nolichucky flows by Nuclear Fuel Services where they may still make all the power rods for the Navy...there have been several MUFs over the years. We used to joke about glowing in the dark after tubing expeditions on the 'Chucky.
There was also the time they shut down the water intakes for Knoxville public water in order to allow a bad spill from Eastman to flow downstream.
Without commenting on the Ohio and upper Mississippi, water quality in LA has also been a concern for years.
I was making a funny and maybe filtration can remove most of the contaminants and I'm sure dirty water is better than none at all. The fact remains, water quality for the whole Mississippi basin is a serious issue.