Swimmers will find eight city-run indoor pools around town (www.ci.seattle.wa.us/parks ):
The very popular outdoor Colman Pool (8603 Fauntleroy Way SW, 206/684-7494) is open summers only for saltwater bathing. The pools at Evans, Queen Anne , and Southwest have saunas, and the Ballard  and Southwest pools have hot tubs.
Green Lake  is a favorite summertime swimming hole, but the water gets a bit rank by the end of the season with algae (lots of nutrients from all the duck and goose poop). Other beaches with lifeguards in the summer include Madison Park, Madrona Park, Magnuson Park, Matthews Beach, Mount Baker Park, Pritchard Beach, and Seward Park. You can also enjoy Lake Washington from numerous Eastside parks in Kirkland and Bellevue.