Well, I think we do harm to our environment. I do a fair bit of backpacking. Unless you are cognizant of pesticide practices in the forest you are hiking, you are taking your life in your hands if you drink from a mountain stream, even if you use a micropore water filter.
And the water downstream of most cities is a real shame.
However, nature is amazing resilient. I conducted a study of a river that had virtually no life downstream of a paper mill. The mill installed a state-of-the-art water treatment system (on their own ... no political pressure) and I was able to study the recovery of the river. It didn't become a pristine river, but within a couple of years there was a remarkable return of flora and fauna to the system.
There was a study in the '60s of a lake that was highly polluted with mercury. The concensus was that the lake would remain permanently contaminated with the element. However, within a couple of years the level of mercury returned to background levels. Even though mercury is an element and will not change to another element, the ecologists were ignoring the fact that a lake is an open system, and the mercury was rapidly moved out of the system through biological movement and through normal dissipation.
