By the time the EPA was created in 1970 most of the heavy lifting of cleaning up the environment had already been done by states and localities.
Pittsburgh was no longer dark at noon, and we no longer poured raw sewage from five cities into Lake Erie.
I had to do a search on the river fires near Chicago - two big ones happened in 1969 (Coyohoga and Rouge River near Detroit). The article said the fires were pretty common.
In 1984 some guy fell in the Rouge River and with it’s raw sewage got some parasite and died. So I’m not sure how active the state’s were in getting stuff done. I think it was just within the past 10 years that one of the great lakes (Lake Michigan?) has developed back into a great sport fishing lake. And some of those rivers are probably still dead.
But - I agree that now that the states know they can have great benefits by having clean water and air, the EPA can be scaled back by a huge amount. I was going to say something about how they might have to deal with larger rivers that flow among numerous states - but ALL the water that hits a state ends up in some major river some day - so that of course is their reasoning for having control over the ditch that runs along the road at the end of our street. (Don’t tell them - the neighbor still filled it up with dirt!)