Lake swimming beach bacteria and temperature - King County, Washington
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Most of our beaches have clear, healthy water. But sometimes a beach can have a problem with poop in the water (high bacteria) or toxic algae this week. Check back each week for updated water test results (mid-May through mid-September). And for now, use the map above to find another healthy beach to swim and play at! Find test results for saltwater beaches on Puget Sound or for toxic algae in lakes across Washington.
Got more questions about our weekly water testing? We’ve got answers in our frequently asked questions section. We test the water for bacteria, which tells us whether there is poop in the water from people, pets, or wildlife. Poop can carry germs that can make people sick from swimming or playing in the water. The bacteria we test for is a harmless type of bacteria found in the poop of all warm-blooded animals like people, dogs, cows, geese, and ducks.
We use the bacteria test results to predict the chance that people will get sick from germs that might be in the water. There are many different types of germs that can come from poop (bacteria, viruses, parasites, etc. ), and it is not possible to test for each one. Instead, we test for one type of bacteria that is easy to measure and is commonly used to predict the risk of getting sick from swimming. Use the table below to explore bacteria results from the beaches you’re interested in.
And see below for an explanation of how to understand these results. King County measures bacteria concentrations at the swimming beaches each week. We collect three water samples from different parts of the beach. Bacteria are measured as colony forming units (CFU), which is a count of the number of bacteria, per 100 mL of water (about a half-cup of water). So what do these numbers mean?
How high is too high? Here’s how to think about the results: Start by looking at the three bacteria results for the day. If there are two or three high bacteria results on the same day, Public Health will generally recommend that people stay out of the water at that beach. If there is only one high bacteria result that day, also look at the 30-day metrics. The 30-day geometric mean is one way to average all the bacteria results from the past 30 days.
If the 30-day geometric mean bacteria is above 100 bacteria/100 mL, or if there are 2 or more high bacteria samples in the past 30 days, Public Health will generally recommend that people stay out of the water at that beach. If there are no high bacteria results that day, Public health will generally say it is OK to swim at the beach. The 30-day m.