Did a trip there in 2004. Did not rate as a "hot" fishing location, but perhaps in early Oct., that could change (I went in July). You can run a loop out of Juniper lake (access out of the Chester area). That part of the park is much less used. Snag Lake is pretty...and abutted by a huge lava field that forms a dam at the north end. There is a trail to a cinder cone north of the lake that is worth a look. Don't bring your pack...lots of sand and shale to get up to the top.
The Hat Creek area will have better fishing for native trout if that is your ultimate goal.