High levels of the potent nerve toxin anatoxin-a were detected in a water sample taken from Anderson Lake on Monday, May 22, prompting Washington State Parks to close the lake for recreation, including fishing, boating and swimming.

The rest of Anderson Lake State Park remains open for hiking, biking and horseback riding. Lake Leland and Gibbs Lake have not shown signs of blue-green algae containing the toxin so far this year, according to a press release from Jefferson County Public Health (JCPH).

Michael Dawson, water quality manager for JCPH, said in an email Tuesday, May 30 that the results of tests are expected by by June 8.

The toxin level is 1.38 micrograms per liter, which is above the state recreational criteria of 1 microgram per liter, the press release stated. The bloom of blue-green algae in the lake contains the toxin-producing species anabaena. Anatoxin-a can result in illness and death in people and animals. Visitors are urged to keep pets out of the water.

JCPH has monitored local lakes for blue-green algae since 2007. Anderson Lake has had closures every year since monitoring began. Last year the closure was exceptionally early, starting April 21. Anderson Lake had been opened by the Washington Department of Fish and Wildlife for recreational fishing on April 22.

To learn more about toxic cyanobacteria monitoring, consult the JCPH website at

jeffersoncountypublichealth.org or call 385-9444.