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King County Swimming Beach Monitoring

If you have question on this site, please contact Debra Bouchard (206) 477-4650.

Swimming Beach Closure Information


Juanita beach closed June 26 due to high count at 0806ESB. It was reopened the following week. Fecal coliform geomeans had been increasing, leading up to the June 26 week. Elevated bacteria counts were attributed to a growing population of geese observed in the area during that time period.

Matthews Beach Off-Leash Area had fecal coliform counts that were high enough to trigger re-sampling on three separate sampling events. Numerous dogs were observed playing in and around the lake on each of these occasions. The beach was not closed as results from the resample the following mornings were low.


There were high bacterial counts at several beaches monitored in Lake Washington (Juanita, Magnusson Off Leash Park, Gene Coulon, Mathews and Luther Burbank) during the 2008 summer season. Only one, Juanita, resulted in a swimming beach closure. Juanita beach was closed in early June for several days.


High bacterial counts at several beaches monitored in Lake Washington (Juanita, Magneson Off Leash Park, Gene Coulon, and Meydenbauer) during the 2007 summer season resulted in swimming beach closures. Juanita beach was closed on September 11th and from August 23rd to 28th due to a broken sewer line in the vicinity.


Bacterial counts at all swimming beaches monitored in lakes Washington, Sammamish and Green Lake in 2006 were within acceptable ranges and did not warrant swimming beach closures.


Bacterial counts all the beaches monitored in Lake Sammamish were within acceptable ranges and did not warrant swimming beach closures. Four Lake Washington swimming beaches were closed in July 2005. Matthews Beach was closed due to high bacteria stormwater inflow from Thornton Creek and was reopened after the streamflow diminished. Waterfowl were suspected as sources of bacteria in the Newcastle and Juanita beach closures. Gene Coulon beach was also closed and although the source of bacteria was not determined the most likely source is waterfowl. There were no sewer line breaks, spills, or leaks, nor is there an adjacent stream that contributes high counts of bacteria into the swimming area.


Gene Coulon Beach was closed on August 24, and remained closed for the rest of the 2004 season due to high bacteria counts. The source of bacteria at Gene Coulon was not determined, but the most likely source is waterfowl. There were no sewer line breaks, spills, or leaks, nor is there an adjacent stream that contributes high counts of bacteria into the swimming area.

Matthews Beach was closed on July 6 due to bacterial counts that exceeded the standards. The exceedances were related to the discharge of urban stormwater adjacent to this beach. The rain storm that passed through the area a few days prior to when the bacteria samples were collected caused increased flows in the stream and increased the discharge of bacteria in many streams. The stormwater from Thornton Creek was the apparent source for the high counts at Matthews Beach, and as those flow decreased, so did the bacteria counts.

Meydenbauer Beach was also closed on July 6. We originally thought that Meydenbauer Beach was closed due to stormwater just like Matthews Beach, and collected additional bacteria samples at the storm drain outfall adjacent to the beach. The bacteria counts in the samples collected at this location were very high and seemed to corroborate the assumption that the storm drain was the source of the bacteria, and contacted the City of Bellevue to inspect their sewer pipe in the area. What Bellevue Utilities found by doing a dye test, was that the sewer line next to the park was leaking, and this leak was immediately adjacent to the storm drain outfall and responsible for the high bacteria counts in the samples collected at both the storm drain and at the swimming beach. The City of Bellevue Utilities carried out exceptionally fast repairs to the sewer line leak. The beach remained closed until these repairs were completed and subsequent bacteria testing showed the counts are low and the waters at the beach a safe for swimming.


The geomean value at Medina Park Beach in late August 2003 was 220 cfu/100ml as a result of the elevated spike of 2000 two weeks prior which was attributed to maintenance practices of hosing goose droppings off of the dock into the water. When these practices were changed to sweeping and removal the counts in the swimming dropped below acceptable levels and the beach remained open.

Meydenbauer Park was closed for one week in early September after a one time fecal coliform count of 5,300 CFU/100ml, and an E. coli count of 5,600 CFU/100ml. The beach was resampled. The resampled data were all <60 cfu/100ml. The possible explanations for this closure could be vessel discharge from the adjacent marina. (In 2004, a broken sewer line was detected and repaired immediately adjacent to the park and could be a possible source of the 2003 elevated counts).

In mid-September after a heavy rainstorm, Idylwood Beach had an FC count of 3100 cfu/100 ml while Idylwood Creek has an FC count of 11 cfu/100 ml. Historically the beach has had two digit counts while the creek has had three digit counts. A count of 3100 cfu/100 ml is not unreasonable for an urban stream after a rainfall. Even with a count of 3100, the 5 day geomean for the beach is 136. The swimming season was over and no additional samples were collected, but the beach would have been closed.


Meydenbauer Bay Beach Park was closed for the 2002 swimming season due to construction on the Lake Washington Boulevard bridge over the park. No water samples were collected.

Green Lake was closed on August 5th, and remained closed for the rest of the 2002 swimming season due a cyanobacteria (blue green algae) bloom. During the bloom concentrations of microcystin, a toxin excreted by the algae, was found to exceed drinking water standards established by the World Health Organization.

The bloom started mid June and a succession of cyanobacteria species emerged throughout the duration. Anabaena sp were the first dominant species. The organisms cells contain both the green pigment, chlorophyll, and a blue pigment that is not evident until the algae are dried; hence the name. These algae readily float and are easily concentrated by the wind. Dried patches of the algae on rocks and concrete along the shoreline look like dollops of "swimming pool paint"

By August 7th the dominant species were Gloeotrichia sp and Microcystis aeruginosa rather than Anabaena . The latter has been shown to be toxic to livestock and cause liver damage in humans. Because of the toxicity, accurate identification is important. Microcystis colonies tend to be bright green and irregularly-shaped: "Flakes and blobs". Microscopically, the cells are densely packed.


Juanita beach was closed for much of the 2001 swimming season due to nearby construction. Juanita Beach had serveral closures in 2000 due to high bacteria levels. There were no closures of King County beaches due to high bacteria levels in 2001.

There were, however, several instances of bathers contracting 'swimmer's itch' in 2001. "Swimmer's itch is an annoying but non-dangerous skin condition sometimes caused by swimming in freshwater lakes containing tiny parasites. These parasites normally live inside waterfowl, such as ducks, geese and gulls. Man is not a natural host but becomes involved accidentally. The small parasites are left on the skin when the swimmer leaves the water and they burrow into the skin, probably stimulated by the drying from evaporation. The parasites then die, causing an allergic, itchy rash that get worse for 2-3 days, then gradually goes away. Although irritating, swimmer's itch is not dangerous, and cannot be transmitted from one person to another. Within 5 minutes to an hour after leaving the water, the person may feel a burning and itching, which can occur on any part of the body exposed to the water. Small reddish pimples appear within 12 hours, and the next day these may turn into small blisters. After a week or so, the itching goes away and the blisters begin to heal. In some cases it may take a month for complete healing." -Pierce County Health Department


There were two beach closures due to high fecal coliform levels during summer 2000. Juanita Beach was closed for a three week period starting July 14, 2000. Crews removed goose feces, employed dogs to chase away geese and utilized pumps to improve water circulation through the swimming area. The beach was re-opened August 4, 2000 after fecal coliform levels dropped. Juanita Beach has had frequent closures in recent years, including a two month closure during the summer of 1998. Large goose populations and lack of water circulaton are the likely causes.

Madison Park Beach was also closed to swimming during the last week of August, also due to high fecal coliform levels. High fecal coliform levels are unusual for this beach and the episode seems to be an isolated incident. Fecal coliform dropped to background levels without intervention.


At the request of the King County Department of Parks and Recreation, the swimming beach areas of lakes Fivemile, Pine, and Wilderness were sampled by the King County Department of Natural Resources for bacteria levels beginning June 17, 1998. On June 20, 1998, the Parks Department and the Seattle-King County Department of Public Health closed Pine Lake's swimming beach because of high fecal coliform bacteria levels. Monitoring of the swimming beach water quality at the three lakes has continued on a regular basis.

Pine Lake was reopened on July 24, 1998 after bacteria levels dropped to an acceptable level. Waterfowl fecal matter is believed to be the primary source of the high counts based on shoreline survey results and the large waterfowl presence at the park. Following is a table of the collected data.