CHIMACUM — Anderson Lake has been closed after water tests found high levels of a potent nerve toxin produced by blue-green algae nearly five weeks after the trout-fishing lake was opened for the lowland fishing season April 22.

Anatoxin-a, which is sometimes produced by blue-green algae, has forced the lake’s closure every summer since 2006. Routine testing of the lake commenced in 2007.

The lake, which is between Port Townsend and Chimacum, is closed to swimming, fishing and boating. Pet owners are urged to keep their pets out of the water.

The 410-acre Anderson Lake State Park remains open to hiking, bicycling, horseback riding and other recreation.

Water samples taken Monday found 1.38 micrograms per liter of anatoxin-a, which is a level above the 1 microgram per liter allowed under state recreational criteria, according to Michael Dawson, lead environmental health specialist for the Jefferson County Water Quality Program, which tests the water in the county’s lakes.

Anatoxin-a can cause illness and death in human and animals within four minutes of being ingested, according to county health authorities.

The closure was announced after the county gave testing results to State Parks, which closed the lake to recreation.

The lake has a bloom of blue-green algae that contains the toxin-producing Anabaena species, according to Dawson.

Fishing has been allowed on and off in Anderson Lake depending on the most recent water test results. While the lake was open for a bit this year, it was already closed due to algae blooms this time last year.

Two dogs died in 2006 after drinking Anderson Lake water. Since then, the lake has been forced to close every year due to toxins.

In 2008, it set a record for the highest levels of anatoxin-a ever recorded, hitting 172,640 micrograms per liter.

This year’s toxicity level of 1.38 micrograms per liter is lower than in the past. Aside from the record-breaking tests in 2008, in 2013, the lake saw levels up to 4.26 micrograms per liter.

Blue-green algae, like that found in Anderson Lake, are naturally occurring and found in freshwater lakes across the state. However, sometimes these blooms produce toxins that are released into the water, though why this happens isn’t fully understood.

Lake Leland and Gibbs Lake — both county lakes — have not shown signs of blue-green algae blooms yet this year, Dawson said.

Anderson, Leland and Gibbs are monitored each month by the Jefferson County Water Quality Department.

Blue-green algae has not been spotted in Clallam County, where routine tests are not done.

Report algae blooms in Clallam County by phoning 360-417-2258, while Jefferson County blooms can be reported at 360-385-9444.

For more information about Jefferson County lakes, visit http://tinyurl.com/jeffersonlakequality or phone the office.

________

Jefferson County Editor/Reporter Cydney McFarland can be reached at 360-385-2335, ext. 55052, or at cmcfarland@peninsuladailynews.com.