A couple of places I fish locally are behind treatment plants. Surprisingly there's little competition.
In the area newspaper, there's been an ongoing conversation of a long gone chicken processing plant and how they used to dump the scrap right into the river. Supposedly the carp (the only survivors at the time) that hung out there were massive. In yesterday's issue one old gent said that when he was kid
to get to best spot, they're just cut right through the processing plant and pick up some bait along the way