When I was in high school and college, we lived in Yardley, PA. The Delaware River was at the bottom of the long hill we lived on, and our neighbor across the street was the head of a research department for Exxon. Exxon gave its employees oil at no cost, at least not to my neighbor. He was always changing the oil in his family cars, and dumping the old oil down the drain in front of his house!!!!
He and I fished together on the Delaware every chance we had. When I was in high school, I thought that the drain led to some mysterious place, and didn't much thought past that. When I found out that it drained into the stream halfway down the hill, and then into the Delaware River, I asked our neighbor to stop dumping his oil into the drain. He went on about the world being made up of chemicals, and that we needn't worry about what environmentalist scare tactics....SERIOUSLY! He was a good guy, but his comfort with oil was not doing the world any favors.
Fast foward close to 20 years, and I ran into my old neighbor at my niece's 16th birthday party. I asked him if he still dumped oil into the drain, and he went on and on about keeping the river clean. He probably did more damage than one person could reverse in a lifetime, but he at least stopped dumping oil into the Delaware.
P.S. I should mention that this section of the Delaware River is NOT the slimey part seen around Philadelphia, and had been transformed once the last of the papermills closed, and other upstream factories stop using the river as their personal garbage can. That's what made my neighbor's oil disposal all the more upsetting.