From the 2018 reg book:
Tualatin River and Tributaries
The following apply to open sections below: *
- Open all year for trout. Harvest allowed May 22 – Oct 31, 2 per day, 8 inch minimum length, remainder of year catch-and-release.
*
Mainstem mouth to Hwy 47 bridge at Gaston
- Open for coho salmon Aug 1 – Oct 31.
- Use of bait allowed.
*
Mainstem above Hwy 47 bridge at Gaston and all tributaries
- Artificial flies and lures only.
So...the section that you wish to fish is open, until October 31st. You can keep 2 trout per day, until then. After that it switches to C & R only.
I've never been out that way. So I'll have to defer to others, for fly selection. As well as how large the resident population is.
Let us know how you do.
P.S. I believe that part of the stream, is
closed to Salmon harvest / retention.