I also like pan fishing. On lake washington, you will do best when you find a 25-35' deep area and fish it at SUNDOWN. There is good fishing from the east side of Mercer Island to Kenndale in Renton.
When bank angling, the arboretum is a fine spot. Again, SUNDOWN is the key. First bite is usually about 7:30 pm and the action will usually be pretty consistent until dark. Three of us went out to our favorite Perch spot a week ago and did absolutely horrible. The standard tear drop weight and worm hook pair usually produces really well when fishing from a boat, but was completely fruitless for us. It was a nice evening and a lot of large fish were showing, but the water temps out there were from 66-68 deg. I think that this might be just a tad bit cold for them.
The best way to "force" perch to bite, is by using a 1/16 smoke grey jig with sparkle and tip it with worm. I found this to be the best producer for perch in the arboretum last July-Aug.
One area that gets a lot of pressure, but provides much action for small perch is the east tip of "Marsh Island" of the Arboretum trail walk. You will also find small blue gills in the lily pads. There are LARGE crappies in these waters as well and a window of time in which to catch a lot of them, but I'm going to keep their secret with me. You'll have to put in your time to figure these guys out. I know I did. I give you one hint, though: You can leave your worms at home. I have never seen someone take these guys on any kind of bait.
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Streams are made for the wise man to contemplate and fools to pass by.
(Sir Izaak Walton)