[AndyS]

Somewhere along the line you will find a group responsible for this stretch of water, it's just a matter of who.
You have an Ameri-Corps Watershed Ambassador attached to that watershed.
You have a Trout Unlimited group attached to that river.
More than likely there is a Watershed/Environmental group attached to that river in those towns.
Do the research and light a flame under their a$$es and you probably won't have to do a thing. THEY need to organize NOT YOU.
BUT with that being said if you ask people to volunteer make sure they realize if they get hurt YOU can't be sued for damages,
Then you have to make prior arrangements with local officials and town DPW for disposal of the trash.
I will see who I can contact, in the mean time MORE photos please !!
How many tires ???