The greater-Seattle area is bounded by the saltwater Puget Sound and freshwater lakes including Lake Washington. In summertime, Seattle sparkles with water activities including boating, fishing and swimming.
Over the past sixty years the greater-Seattle metropolitan water treatment program has led to better water quality in Lake Washington, and yet every summer there are some “closed beach warnings” because of high bacteria levels or toxic algae in the water.
This blog article will list the reasons for water contamination in Lake Washington and will describe the water-quality monitoring efforts of the metropolitan district (King County) and the citizen activist group, Thornton Creek Alliance. You can meet & talk with the volunteers of Thornton Creek Alliance at their display table on Saturday, August 1, 2026, at the Lake City Summerfest.









