I comprehend just fine. I recognize that the private companies polluted the river in the first place with no regard for the damage they were doing to the environment. That's the bottom line and addresses your original claim that there is no need for government intervention because the private companies will protect the environment on their own. History has proven this to be false. Maybe since it was before you were born, you don't believe it happened, I'm not sure?
And the Cuyahoga River is just one example of negligence regarding environmental destruction by unchecked actions of the private sector.