It is worth noting that Seattle Municipal code outlaws swimming beyond 50 feet from a shore without an accompanying kayak or boat. Police have ticketed open water swimmers at Green Lake in the past.
I'm a little miffed but understand why you skipped the Shoreline pool, we're not exactly in Seattle. And there's a fantastic pool in Lynnwood that has been thoroughly remodeled and is such a blast, yet again, it's not Seattle. Thank you for a great article.
You forgot a couple lakes, both in the north end (but definitely in Seattle): Haller and Bitter. Both are pretty easy to get to by bike, via the Interurban Trail (Bitter Lake is really easy to get to that way).
And public swimming pools? Bletch!
If you gaze up at "hydroplanes" landing on Lake Union, you're about to be crushed to death by an airborne, high-performance watercraft.