PORT TOWNSEND — Anderson Lake is still poisonous but to a lesser degree than earlier this summer.
The most recent samples from the lake between Port Townsend and Chimacum, which has been closed since May 3 because of high levels of a deadly nerve toxin, contained only 22 micrograms of the toxin anatoxin-a per liter of water.
That’s only 22 times the safety threshold of
1 microgram per liter.
“It sure is a lot better than 619” micrograms per liter, the level tests found in samples the first week of July, said Greg Thomason, Jefferson County environmental health specialist, Friday after test results were received.
The lake remains closed to all recreational use, while other lakes tested last week — Gibbs Lake and Lake Leland — are safe.
Only the lake is closed in Anderson Lake State Park. The 410-acre park surrounding the lake remains open. A Discover Pass is needed to park there.
The decrease in anatoxin-a is typical for the time of year, Thomason said.
“The normal pattern is that the level of anatoxin-a peaks in May or June and drops off now,” he said.
As anatoxin-a drops off, microcystin — another algae-produced toxin found in East Jefferson County lakes — tends to rise, Thomason said.
“From mid-August to mid-September, microcystin will rise and peak out,” he said.
Microcystin typically “comes later in the season.
“We’ll see if it follows the regular pattern or not,” he said.
Anatoxin-a acts quickly and can cause paralysis and stop breathing.
The most severe effect of microcystin is that some people could develop liver failure if they have consumed water containing the toxin over a long period of time.
Its short-term effects can include nausea, vomiting, diarrhea, skin irritation and burning, abdominal pain, blistering in the mouth and sore throat.
Both toxins are created by certain species of blue-green algae.
Researchers know that warm weather fuels algae growth when sufficient nutrients such as phosphates are present, but they don’t know why algae that is usually benign will suddenly begin to produce toxins.
No anatoxin-a was found last week in either Gibbs Lake, a popular swimming hole south of Port Townsend, or Lake Leland, north of Quilcene, Thomason said.
Only a trace of microcystin was measured last week in Gibbs Lake, where the level was high enough to prompt the posting of warning signs four weeks ago.
The level in Gibbs Lake then was 7.9 micrograms per liter. The safety threshold for microcystin is 6 micrograms per liter.
Since then, the warning sign has come down at Gibbs Lake.
But Leland — where no microcystin was found last week — and Gibbs remain posted with caution signs because both lakes contain the type of blue-green algae known to produce toxins at times.
Weekly test results are announced Fridays after samples are taken Mondays.
No toxic blue-green algae has been reported in Clallam County, where health officers do not test for toxins; instead, they visually monitor lakes for signs of algae bloom.
Report algae blooms in Clallam County by phoning 360-417-2258.
Report algae blooms in Jefferson County by phoning 360-385-9444.
For more information about lake quality in Jefferson County, visit the environmental health website at http://tinyurl.com/6z64ofy.
Managing Editor/News Leah Leach can be reached at 360-417-3531 or at leah.leach@peninsuladailynews.com.