Like Rog said, stop at any of the "quiet walkways" and hike down to the river from there. The paths are not too tough. But once you get down there and start fishing upstream, you have two options: 1) backtrack to catch the path up to the parking area, or 2) scramble up the bank to the road and then walk down the road to your car.
The second option is a bit dicey in that there are several places where the road is quite aways above the stream and there is no path up, in other spots its not so bad.
I would also recommend wearing long pants (or waders) if you are going to scramble. There is a plant that has some form of skin irritant that if you brush up against it, in about 15 seconds it feels like you walked through thorns. It took me a few times before I realized which plant it was and could steer clear of it, but its all up and down the WPLP (probably in other parts of the park, as well), but if you wear long pants, its not a bother...
"Even a fish wouldn't get into trouble if he kept his mouth shut."