Try it, there are a bunch of bass in that area. Not sure how many are in the Tualatin. That area is fairly tight, there are a lot of people loading/unload SUPs and yaks where would want to fish. Above that there is a lot of private property to mindful off. My thought is it be a tough cast to get a bugger where you'd want it.
Lots of fish in the Willamette near that location. My read is that fish aren't going to fight any extra current and hold in the Tualatin. Check out reports for the user Bass, he fishes that area a lot and has very detailed reports.
If its in the budget your have a better chance from a flotation devices.
Fly fishing Portland proper is tough, no trout in area. Bass fishing is better on the water then from the bank all along the Willamette.