PORT TOWNSEND — The state Parks and Recreation Commission has closed Anderson Lake after monitoring by Jefferson County Public Health revealed dangerous levels of Anatoxin-A.

Water-based recreational activities such as fishing, boating and swimming are prohibited until the bloom dissipates and the toxin levels decline.

Anderson Lake State Park remains open for other activities, such as horseback riding, hiking, biking and birdwatching, but visitors should avoid the lake.

Anatoxin-A, sometimes called “very fast death factor,” is a potent neurotoxin produced by cyanobacteria that can cause sickness or death when ingested in even small amounts.

Samples of water taken from Anderson Lake on April 22 tested by the state Department of Ecology revealed Anatoxin-A concentrations of 90.3 mcg/l, which is 90 times higher than the state’s recreational criteria allow.

The samples also showed traces of microcystin toxin that where much lower than the 8 mcg/l level allowed by the Department of Health.

Toxin levels for lakes in the state are posted at www.nwtoxicalgae.org.

Public Health has monitored lakes in Jefferson County since 2007 and Anderson Lake has been closed every year since then.

Although no human exposures have been documented at Anderson Lake, the deaths of three dogs have been confirmed to be due to Anatoxin-A exposure from the lake.

Anderson Lake has been sampled weekly since April 1, when algal blooms were first identified.

Public Health also monitors Lake Leland and Gibbs and Crocker lakes weekly, but no algal blooms have been seen in any of them.

Tarboo Lake was also checked on April 27 prior to the state Trout Derby, but no blooms were seen.

For more information, call Environmental Public Health at 360-385-9444 or visit www.jeffersoncountypublichealth.org/723/Lake-Status.