I know the creek
extremely well as well as the branch line. I also know NS.
Tick them off and you won't be walking along the tracks to move along the creek for long and there will be nothing you can do about it.
Like it or not, walking along or on those tracks IS trespassing and NS would be within their rights to make an arrest for such with their own LEO's. Whether they would bother is up to them but it IS their property. It doesn't belong to the public or the folks whose property overlooks the line.
I'm sure none of those outraged property owners would appreciate a stranger taking upon themselves to come on their back lawn to pick up something the interloper considered an eyesore...
If you want to approach the situation intelligently, contact NS and express your concern. I have posted a portion of the Cement Secondary track map from the junction with the Lehigh Line to Center Street which more than likely covers the area where you saw the "litter." It has the sections defined as well as listing all of the crossings. That should help you adequately describe to NS where you saw what.
If you call you may find out the debris is scheduled to be picked up at a later date as is done with discarded ties & tie plates. That may not be soon enough for the folks who want to clean up litter on someone else property but it's how railroads do things.
If you want to stir the pot, do what you want.
And again, IF the creek has been impacted because of this (which I doubt), contact the PFBC.