I talked to a retired fella from the DNR a long while ago. He was telling me, back in the ’70’s, the nets in Pool 1 they used for counting fish, never had fish in them, just pieces of toilet paper. The Clean Water Act changed that dramatically.
The sanitary systems were connected with the storm sewer systems. When it rained, the sanitary sewers over filled the plants and the raw sewage went directly into the river.
The good thing for us is that sewage is biodegradable. With a little time, it’s gone. Unlike mercury, PFAS/PFC, theses last for ever (although some is swept down stream).
I’m no expert, I know just enough to be dangerous and not enough to be dangerous.