Collaboration in Civic Spheres

King County Beaches – Fecal Coliform Bacteria Data

by Matt Rosenberg June 28th, 2010

BACKGROUND: The King County Water and Land Resources Division monitors levels of fecal coliform bacteria in the water, plus algal toxins and water temperatures at a total of 28 swimming beaches or creeks in King County – including several in Seattle on Lake Washington. Beaches and creeks are limited to those under jurisdiction of County’s freshwater program. From the week before Memorial Day through the week after Labor Day, the division posts weekly reports at a special Web site which prospective visitors can check before choosing a beach at which to swim. In the last 12 years, the county has posted closure notices 16 times for elevated bacteria levels and once for algal toxins.

Except for a recent closure at Hidden Lake in Shoreline, all those are catalogued in this historical summary of closures which includes locations and causes. Six were at Juanita Beach in Kirkland, three each were at Meydenbauer Bay Beach in Bellevue and Matthews Beach in Seattle, two at Gene Coulon Beach in Renton and one at Madison Park Beach in Seattle. Beach users can also review the full history of readings for a beach, at the historical monitoring data page. Select a beach and then “all years” from the pull-down menu.


Whenever reported fecal coliform or algae toxin levels are in the moderate concern category, the results are marked with a yellow overlay; red means closure notices were to be posted. According to the Division’s FAQ page, “fecal contamination from waterfowl, dogs and cats, surface run-off from poorly drained grassy areas adjacent to the beach, high concentrations from nearby creeks, and poor water circulation in the swimming area may contribute to the high bacterial counts.” Other causes identified include storm water inflow, hosing goose droppings off docks into the water, and discharge from a vessel in an adjacent marina. When swimming water has highly elevated fecal coliform levels then accidental ingestion by swimmers can heighten the risk of gastrointestinal distress. Separately, presence of blue and green algae can lead to development of nerve toxins in swimming water, which can cause respiratory and other problems.

King County Water and Land Resources Division, Database of historical readings and current weekly reports on fecal coliform bacteria, algal toxin levels and water temperature at King County swimming beaches and creeks. So far in the 2010 season, concerns have been confined to eight sites. Yellow levels have been reported 11 times altogether, and one closure notice posted.

Echo Lake, N. 200th St. and Ashworth Ave., Shoreline, (results);
Hidden Lake, NW Innis Arden Way, Shoreline, (results);
Houghton Beach, 5811 Lake Washington Blvd., Kirkland, (results);
Idylwood Beach, 3601 W. Lake Sammamish Way, Redmond, (results);
Idylwood Creek, 3601 W. Lake Sammamish Way, Redmond, (results);
John’s Creek, 1305 Lake Washington Blvd., Renton, (results);
Marina Park Beach, downtown Kirkland, (results);
Matthews Beach, 9300 1st Ave. N.E., Seattle, (results);
Thornton Creek, 9300 1st Ave. N.E., Seattle (results).

Closures occur after a high individual weekly reading leads to repeated samples which yield a “geometric mean” (weighted average) of 200 fecal coliform CFUs (colony forming units) per sample, with no single sample exceeding 1000, or if additional sampling shows a single reading of 1000 CFU or more.

RELATED: Additional beaches in Seattle and counties other than King in Western Washington are monitored for public health and water quality safety through the Beach Program of the Washington State departments of Ecology and Health, although the measure is for a different bacteria, interrococcus, which is a better indicator of gastrointestinal health risks in saltwater. No beaches are currently closed for swimming, but several are on the advisory list, at this writing, with a “yellow” status meaning bacteria levels exceed EPA recommendations and children, the elderly and sick should stay out. The state’s Beach Program also monitors and reports which beaches are unsafe for shellfish harvesting, there are many. Always check the page for “Recreational Shellfish Beach Closures Due To Biotoxins Or Pollution,” which is updated regularly.

King County also provides data on open water drownings and prevention.

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