i don't know how far up they run the river. You can access an upper stretch of the river via martens road if you have a good 4x4. The lower part, you can park near the trailer for construction and fish around the bridge there or walk south to the train bridge.
Or just go a little past on the highway, turn right on to mountain bay road, turn right immediately after crossing train tracks, following the little road next to the tracks. There's a spot to turn around/have a fire/ launch a canoe at the food of the train bridge, and it allows you to fish a nearby pool etc. Hope that helps :).