It bothers me when people make a mess and just leave it, especially when it's near a body of water. I'm always disappointed when I see the amount of garbage left behind by lazy people - I'm not a "granola-cruncher", "tree hugger", or whatever term you want to use, but I care about our earth. I recycle, we cloth diaper our daughter, I turn lights off when we're not in the room.
I think it's great that people are active outside, but please just clean up after yourself.