The water they fish (West Branch Lackawaxen) is pretty good only because they stock it. The very upper reaches used to be stocked by the Fish Commission but I don't think they are anymore since the hatchery(Pleasant Mount) isn't a cold water hatchery anymore. Actually I'm not sure what they do there.
Summer water temps in the entire Lackawaxen usually get too warm for trout fishing although on occasion I see it being fished where it passes under Rt 247. There is a USGS gauge(Aldenville) right there that includes the temp so there is really no excuse for it.
This section of the WB Lackawaxen is more small stream than river. I've not fished this section but it's only 10 minutes from my house so I drive past the area frequently.
There is another fishing club on the WB Lack downstream from this one. Between the 2 of them some nice trout end up in Prompton Reservoir. The WB Lack going into Prompton is private except for the last 1/2 mile, probably less, where you're on state park property. The trout don't know that though and a few big ones have been caught just inside park property. I've heard of people being hassled by club members years ago but if you catch fish on state property there's nothing they can do.