I usually launch at Sayres Pits (just southwest of the I-90 bridge) or Atlantic City (by Rainier Beach High School). There is also Gene Coulon Park (by Boeing in Renton).

I don't fish for perch on the lake so I can't help ya there.

Trout, you will usually find in the top 30' of water. When the smolt are flushing out of the Cedar River they ('bows & cutts) will be on the surface chasing those smolt. Find smolt, find big cutts and 'bows.

Fishing around the bridges (I-90 & 520) is always a good bet. The south end of Mercer Island and near the Cedar River are good too.

Like Zen said, get the latest issue of Fishing & Hunting News. There is a good map of Lake WA for you to study.
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Carl C.