My dad's fly fishing club, the Fly Fishers of OC, seem to think that place is real good. I'm not too on it myself, but I know it holds under 10" fish pretty good. I believe you need to do some moderate hiking to get to the good water.
I can't believe the water is very deep or wide, so I don't know about the nimphing thing...but you might get some little guys on small dry flies.