The Yakima river is a world class trout fishery. The are many guides that work the river. You will float in a drift boat or raft and fly fish for Rainbows. The Columbia river is a 30 minute drive as well and there is a great fall Salmon fishery for kings to To 4Olbs in the Hanford reach . The last free flowing stretch of the big river. You can also fly fish the Naches river . It low and clear right now and the trout are small but it has lots of access from the road. You can drive a hour from Yakima up the Naches river and end up at Mt Rainier. There are also lots of small lakes and ponds near Yakima that you fish from shore. Yakima can be pretty low rent and most of the places you will fish your self will be crowded with illegals on a weekend. Lots of info on the web. Start here and search . If you post in the Firums you will get lots of info on guides etc. someone may even offer to take you out. I would but I am out of town most of Sept.
Too soon for Salmon on the Columbia, but that area is know for excellent Walleye fishing.
While your there I would recommend doing a day trip up hwy 12 to Packwood and on to Mt Saint Helens, you could reverse course of do the loop back to Trout Lake etc.. on back to Hwy 4 and back to Yakima going thru Goldendale. You will see some a very diverse and stunning scenery.
Was at Yakima training center doing fire suppression in the late 90's and one of the civilians in the motor pool took us where two rivers came together and we brought home two coolers full of catfish after the night fishing. All I can remember is it was the Yakima river and another.....