OK Aquaman I'm going to correct some of the things you said that are totally invalid. ie wrong and misleading.

You can't just look the water and tell what's in the water even if you are a scuba diver. Scuba divers are not Chemists. And only a chemist using sophicated analytical equipment can tell whats dissolved or suspended in the water.

Fish can't clean themselves of PCB's and Mercury and other heavy metals by swimming in a tank of clean water. That's not going to happen.

The visibility of the Ohio River at the bottom is ZERO. I too was on a dive team for many years and have dove in the Ohio River on recovery operations many times. You can't see your own hand in front of your face mask when on the river bottom. Beside the current is so strong that you can barely stay orientated down there.

BTW the river bottom slow the current down so the current right next to the bottom is slower than a few feet above the bottom or in the middle of the water column. Just like the current next to the bank is slowed down by the friction between the water flow and the land. Current is slowest near the bottom and thus the visibility is better. Even then the visibility at the bottom of the Ohio River is zero on most days. Perhaps if there is no rain for a month or two and the river is very low and with no flow it might clear up a bit. But then the sewage being dumped into the Ohio River is not diluted by the rain water and the concentrations of chemcials in the river is increased.