I could give an official opinion on this, but I'd have to charge you my usual rate of only $150/hour. The Rogue hit it on the head. There MIGHT be a prescriptive easement here, tho it's hard to tell from the facts presented. And you would, indeed, have to go to court to prove it.

I guess I'd look at this way: if you had a house on the river, would you want people traipsing through your back yard to get to your honey hole?

Now, the river itself is public property. Perhaps you should invest in a good sled and launch on public property.

P.S. You think you got it bad in Western WA, try driving across the Hanford Reservation some time where guys with Uzis will put the stop to you!