That's because it's not really a river. It's the Sammamish Slough. I'm not sure what jack hole(s) decided to start calling it a river. It's basically the flat / frog water between Lake Sammamish and lake Washington. The elevation drop if I remember correctly is less than 30 ft., that does not equal fast water. Outboard and Hydro races used to be held on it. Now that was a good use of the water way! Any way it can be a good place to fish, just pick a spot where any road goes over it and hit the Burk Gilman and go as far as you want. Remember to read the regs and understand them, there's a lot for that stretch of water and pay special attention to the C&R rules and handling.
Build a man a fire and he's warm for the night. Light a man on fire and he's warm the rest of his life!