I like the bald eagle comment.. that's some truth.
The only time I've made the drive out to Big/Gnat creek I watched and followed a bald eagle while it circled and surveyed Gnat Creek. Hiked in quite a ways.. then lost him around a corner that was overgrown and I couldn't keep up. Once I came around I saw him sitting on the top of a tree looking down.
He was staring at a hole filled with 10-12 fish, the first time I had ever seen something like that on such a small creek. They were all too far in to spawning, but I learned what "Alm21" is talking about. Eagles = Fish. Also, he didn't bother swooping in to any of them. I think he even knows the good vs. bad meat.
I've also figured out that watching the sea lions on the Willy can tell you if you're wasting time. It seems like they'll just move through if there's no fish. I watched one go through the entire Clackamette/Meldrum area, up to O.C., back down then up in the Clack to the 99 bridge and back out.. Then he left. Needless to say no one caught anything that afternoon.
It's nice having natural "fish finders"... Especially when you're bank bound.