To consistently catch trout in Lake Washington, depth control is a must. Leaded line is an inexpensive alternative to downriggers that is very effective. The only exception is during mid-summer, when most fish are caught between 45 and 60 feet, beyond the range of (most) leaded-line rigged rods.
Try this. Leaded line, (12 or 14 pound test) 30-40 feet of 10 test leader.
Needlefish in size 2 or 3. Nickel/Red, Brass/Red, Clown (yellow with red spots) or 3.5 inch Coyote spoons in army truck, watermelon or greenglo.
Put out 4 to 5 colors of line. Sink rate is approx. 6 feet per color. Troll fairly fast (1.7-2.2 mph) Get yourself a fishfinder.
Juanita Bay is great place to start.
Tell me what kind of boat you have and I'll keep an eye out for you. Make sure you have/wear a PFD, it can get surprisingly rough.