2 Seattle beaches test for unsafe bacteria levels

Officials are urging people in Seattle to stay out of the water at two beaches after they tested for unsafe bacteria levels.

On Wednesday morning, King County officials advised the public to stay out of Andrews Bay Beach in Seward Park and Idylwood Beach due to high levels of bacteria.

Lakes around Seattle are crowded with people as the heat has intensified over the past several days. The King County website provides weekly updates on the water quality of swimming lakes to notify residents of unsafe bacteria levels.

How often are bacteria levels tested in King County lakes?

King County officials test the waters for bacteria weekly. Any time there is high bacteria, it likely means the beach has a problem with the amount of feces in the water. 

How do they test for bacteria levels in lakes? 

Every week, officials collect three water samples from different parts of each beach. "Bacteria are measured as colony forming units, which is the count of the number of bacteria, per 100 mL of water," officials said on their website

After completing the tests and looking at the results, county officials will determine if bacteria levels are too high. If two or three samples come back with high bacteria levels, then the beach will be considered unsafe for swimming. If one test result comes back as high, officials will use a ‘30-day metric’ to determine if the average bacteria results from the past 30 days are above 100 bacteria per 100 mL. If so, Public Health officials will recommend people stay out of water.

This last week, Seward Park’s Andrews Bay Beach had a bacteria sample that tested at 540, and Idylwood Beach had three samples that tested over 500. 

For more information on testing and quality of swimming water, please visit the King County website.


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