Here is another thing to consider when weighing this out, or trying to define laws that are a little grey.....What are the possible consequences?
I also see your point about the laws, I read more on that last night and....You may be right! According to the one link, you have to stay 50 ft or a quarter of the water way from the property. If that link is correct....
I know you are chasing law, I also know what I would have personally done at one time, But I have this thing with private property, whether it be a claim,or whatever. This is what might eventually cause it all to go off limits, By law. When people start pushing "their rights" on a property owner. I personally do not agree, And just out of principle? Would probably fight it or make it real rough on someone throwing that around in the middle of my land if I asked them to leave. If I was in that mood.

But on the flip side, I respect property owners and if were confronted, legal or not through a stack of rules and laws, would probably apologize and move on instead of reciting some laws. This also depends on the size of the stream too!
Is it hurting anything? Hell no, and most people would care less! I walked creeks for miles and looking at rocks, arrowheads and whatever, I was only confronted once in a negative way, and after talking and the guy calmed down, he was fine. He was just worried more than anything.
How you treat people when confronted goes a long way too!! Reciting laws? Might not be the way to do it in cases like this.
Then back to...What are the consequences, probably not much, if your peaceful. Worse case is asked to leave.
Anyhow, just my ramblings, law or not, I'm kind of mixed on this subject. They give you more rights to be doing it on private property,without permission, than they do on public? THAT MAKES NO SENSE TO ME!!!!
Not that any of it hurts a thing! I get that....I'm a "Rights" guy too!! But property Rights out weigh, on this stuff in my mind, I feel the owner should have complete say on what goes on, on his land in these cases.