Anderson Lake waters closed for toxins

Kirk Boxleitner
Posted 6/12/18

Anderson Lake is currently closed until further notice, after toxins were found in its waters May 29.According to Michael Dawson, water quality manager for Jefferson County Public Health, high levels …

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Anderson Lake waters closed for toxins


Anderson Lake is currently closed until further notice, after toxins were found in its waters May 29.

According to Michael Dawson, water quality manager for Jefferson County Public Health, high levels of the nerve toxin anatoxin-a were detected in a water sample taken from Anderson Lake that same day.

Dawson reported the toxin level was 112 micrograms per liter, above the state recreational criteria of 1 microgram per liter.

Dawson elaborated how the bloom of blue-green algae (also known as cyanobacteria) in the lake contains several toxin-producing species of algae, including Dolichospermum (formerly Anabaena). Because anatoxin-a can result in illness and death in both people and animals, Dawson notified the public that the state parks have closed the lake for recreation, including fishing, boating and swimming.

“Visitors are also urged to keep pets out of the water,” Dawson said. “The rest of Anderson Lake State Park remains open for hiking, biking and horseback riding.”

While blooms have also appeared at Lake Leland and Gibbs Lake this year, Dawson noted toxins have not been detected at either of those lakes so far in 2018.

JCPH has monitored local lakes for cyanobacteria since 2007, and Dawson pointed out Anderson Lake has had closures every year since that monitoring began.

“In 2017, the Washington Department of Fish and Wildlife made changes to the fishing season at Anderson Lake, to allow recreational fishing during the colder months, when blooms are less likely to occur,” Dawson said. “State parks also opened the Anderson Lake gate on a Friday-through-Sunday schedule from November of last year to April of this year. Although late season blooms kept the lake closed through last fall, the early part of this year saw five consecutive months of open access.”



Dawson explained how excess nutrients in water, such as nitrogen and phosphorus, along with sunshine and warm temperatures, are among the “major factors” causing algae blooms.

“Lack of water circulation or mixing, and lack of grazing by zooplankton can also be factors that allow the runaway growth of these microscopic organisms,” Dawson said.

While algae blooms can come in a number of varieties, including freshwater and saltwater, Dawson reiterated Anderson Lake had shown evidence of a freshwater cyanobacteria, or blue-green algae bloom.

“It's still a puzzle as to why Anderson Lake is so toxic, but the lake does have very limited circulation, which keeps the nutrients in and lets the algae grow,” Dawson said. “We don’t have any local data on cyanotoxins in streams or bays in Jefferson County. There have been studies in California, linking freshwater blooms to the presence of toxins in mussels in San Francisco Bay and Monterey Bay, but those were carried by rivers much larger than the outlet of Anderson Lake.”

Dawson clarified there are other kinds of harmful algae blooms, “often caused by dinoflagellates and other species,” in saltwater causing shellfish closures, but they are not harmful to swimmers. 

The public can check on those by visiting this map:

Likewise, studies have shown how some cyanotoxins, such as microcystin, can accumulate in fish livers, which Dawson acknowledged can cause problems “in parts of the world where people eat large amounts of small fish whole.”

Dawson reminded residents the state Department of Fish and Wildlife recommends cleaning fish well, and discarding the guts, when eating fish from a lake that may have a cyanobacteria bloom.

“Fish can also die when decomposing algae blooms rob a water body of oxygen,” Dawson said. “So far, oxygen levels at Anderson Lake have not gotten that low.”

Indeed, Dawson summed up the algae blooms at Anderson Lake as “pretty consistent” for the past 10 years.

“The lake usually closes between April and June, and doesn't get better until the fall,” Dawson said. “This year was actually a little later than normal for a closure. However, algae blooms seem to be getting worse around the globe. They're more frequent and more severe in many places, and warming temperatures are known to be a factor, along with water pollution.”

To check the status of Jefferson County Lakes, and learn more about toxic cyanobacteriamonitoring, call 360-385-9444 or visit the JCPH website at:

For fishing seasons and regulations, visit the Department of Fish and Wildlife website at:

Information on visiting Anderson Lake State Park is available online at:    


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