The Copalis is a small coastal river that is mostly very brushy on both banks. I don't consider it very fly fishing friendly. That's not to say it cannot be fly fished, but the spots to do so may be widely spaced. I've never fished it. A couple friends have fished it, for sea run cutthroat in Sept. & Oct. and coho salmon in Oct. & Nov. It gets a small run of winter steelhead as well. The Copalis is gillnetted by members of the Quinault Indian Tribe.
If I were going to be in the Copalis area and wanted to do some fishing, I'd fish the Quinault or Queets Rivers, for better fly water and better prospects. The Humptulips is not far from the Copalis, but I've found it not to be very good for fly fishing either, except for sea run cutthroats in Sept.
If you're planning to be in the area and want to fish, PM me including when you will be here, and I'll give you the best suggestions I can.