Swim Beach Monitoring Program

Luther Burbank and Groveland Beaches are the two swim locations tested on Mercer Island.

The City of Mercer Island's water quality testing program has been in effect since 2003. The results typically show very low quantities of bacteria in the water at our beaches. Water is tested weekly by King County staff for bacteria during the swim season (mid May through early September) and results are posted on the King County testing website.

If a test location exceeds standards, the City would also post notices widely at that beach.

Water Quality Testing Formula

Click here to view King County's closure criteria

Definitions:

  • CFU’s (Colony Forming Units) are a unit of measure. After incubation, bluish colonies of bacteria should appear on the sample dish. It is then necessary to count all of the colonies that are in each dish. A calculation must be performed to determine the number of colony forming units per 100 milliliters of sample.
  • E-Coli: One of hundreds of strains of the bacterium Escherichia coli. Although most strains are harmless and live in the intestines of healthy humans and animals, this strain produces a powerful toxin and can cause severe illness.
  • Fecal Coliform: Bacteria from excrement, fecal coliform are not necessarily harmful by themselves, but are indicative of the presence of other disease-causing organisms that may cause diarrhea, vomiting, or a more serious illness.

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