I don't fish in Pennsylvania, but I suspect that most of the major rivers in the other states are in the same shape on their lower reaches. The problem is urbanization requires sewage collection and treatment, rather than the environmentally ideal septic tanks. Treated sewage still has all the toxics that were in it before it entered the plant. Biological treatment cannot remove those chemicals that are toxic to the bacteria that do the treatment, and the cost of chemically treating the massive flow that most urban plants handle is beyond reason. For this reason, and likely no other, our rivers are toxic sewers by the time they reach sea level.
This is the price of living in cities. We could do far better if we were spread out on the land, and there many pre-filtration systems that can be applied to septic systems to assure that the cleaning products, and industrial chemicals do no harm to the bacteria in the tank.
Ah, but where would socialism be if Americans lived all across the land, each with a home and some independence?