Department of Health: Lake Pleasant okay for rec use

  Lake Pleasant algae bloom

Lonnie Archibald photo
A blue-green scum lines the shoreline of Lake Pleasant recently.  Samples have been sent to the Washington State Department of Ecology to be analyzed.

The Clallam County Department of Health and Human Services released on Thursday, Jan. 24 a report on the dangers to humans and animals from an algae bloom in Lake Pleasant in Beaver.


Lake Pleasant Algae Bloom

Source: Clallam County Department of Health and Human Services

CA blue green algae bloom has been detected in Lake Pleasant in Clallam County.  Testing on a sample collected on 1/16/13 has detected very low levels of the toxins Microcystin and Anatoxin-a.  The level of Microcystin is 0.0645 mcg/L.  Water becomes unsafe for recreational use when levels exceed 6 mcg/L, almost 100 times the level detected in the Lake Pleasant sample.  Microcystin in high doses can cause liver damage.  Low levels of the neurotoxin Anatoxin-a were also detected in the water sample.  Anatoxin-a levels were measured at 0.0201 mcg/L.  The recreational closure level for anatoxin-a is greater than 1 mcg/L, about 50 times the level detected in Lake Pleasant water.  Anatoxin-in high doses is a potent neurotoxin and can cause paralysis, seizures, and respiratory failure.  Boiling of water does not inactivate either microcystin or anatoxin-a and special treatment is needed to remove the toxins from water.


Additional testing showed that the cyanobacteria species Aphanizomenon was the predominant type of blue green algae detected and another type of cyanobacteria called Anabaena was present.  Aphanizomenon is typically associated with Anatoxin-a production while Anabaena can produce both microcystin and anatoxin-a.   Blue green algae come in both toxin and non-toxin producing forms.  The testing results from Lake Pleasant indicate that most of the blue green algae is of the non-toxin producing form, but a small percentage is capable of producing the harmful toxins.


Based on current test results, Clallam County Health and Human Services is recommending no restrictions on recreational use of Lake Pleasant at the present time.  The greatest risk of toxin exposure comes from ingestion of the blue green algae itself and animals should be restricted from drinking from the lake when blue green algae is visible on the shore line.  It is unusual for blue green algae blooms to occur during winter months.  They are more common during Spring and Summer when warmer weather and longer periods of sunshine encourage their growth.  Types of algae and levels of the toxins they produce can vary from week to week.  Algal blooms in Lake Pleasant will be monitored during the Spring and Summer to assess the safety of recreational water use during those periods.

Additional information on toxic cyanobacteria can be found at: 

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