PORT TOWNSEND — The level of a potent nerve toxin in Anderson Lake has soared to more than 100 times the safe level.
The skyrocketing level of anatoxin-a in the lake — which will remain closed to all recreational use, though the state park around it remains open through October — is unusual so late in the season.
“This is a dangerous level of anatoxin in the lake at this time,” said Michael Dawson, water quality lead with Jefferson County Public Health Department, on Friday after test results were received from samples taken Monday at the lake west of Chimacum.
“We don’t want people to let their guard down just because it’s fall,” he added.
The latest sample tested contained 102.3 micrograms of the potentially deadly anatoxin-a per liter of water.
The safe threshold for the toxin created by blue-green algae is 1 microgram per liter.
The newest test results are a huge jump from those of the week before, when the level of anatoxin-a, which can cause paralysis and stop respiration, was measured at 15.3 micrograms per liter — still 15 times the safe level.
The week earlier, the level was just above the safe threshold, at 1.43 micrograms per liter.
Lake stayed closed
And prior to that, the levels of the toxin had been so low for two consecutive weeks of September that the county public health department had recommended reopening the lake — which had been closed most of the summer because of elevated toxin levels — though Mike Zimmerman, ranger in charge of the state park, decided against that move and kept the lake closed.
The upward trend in lake poisons as days grow shorter and cooler is almost unprecedented, Greg Thomason, Jefferson County environmental health specialist, said two weeks ago.
Algae growth is fueled by sunlight and nutrients such as phosphates. Generally, as algae dies off in the fall, the level of toxins slows, as well.
Thomason said then that the atypical rise could be because of a genus of blue green algae, coelosphaerium, which until it was discovered in a sample from Anderson Lake taken Sept. 10, had never been seen in any East Jefferson County lake.
Coelosphaerium can at times produce anatoxin-a, just like the toxin-producing blue-green algae typically found in the county’s lakes: anabaena, aphanizomenon and microcystis, the latter of which also can create microcystin, which can cause skin irritation and nausea over the short term and liver damage if ingested over a long period of time.
“We don’t have more information on [coelosphaerium] yet,” Dawson said, adding that no updates on the types of algae in Anderson Lake was available as of Friday.
Algae, which are colonies of microscopic plants, can be spread between lakes by waterfowl or other means.
“We don’t really have an idea of why the anatoxin is increasing,” Dawson said.
Algae could be getting better fed, with “mixing” of the lake bringing nutrients up from the bottom to the surface.
Lakes often “turn over” in spring and fall because of changing temperatures, Dawson said.
In summer, there is stratification, with the upper level warmer than the water below. In that upper level, algae may use up available nutrients and die off. But then, when temperatures cool, the water sinks, and the levels in the lake mix.
It could also be that there has been a change in the composition of the species of algae and one is more favored at this time of year, he said.
“There could be a whole number of factors,” Dawson said.
“It’s not well-understood why toxins appear sometimes and not other times.”
Anderson Lake has a heavy bloom with scum.
Only a trace of microcystin was found.
Other lakes
No anatoxin-a and only a trace of microcystin were found in Gibbs Lake, which has a heavy bloom and scum.
“We’re recommending people try to avoid contact with the scum,” Dawson said.
“Those scums tend to concentrate the toxins.”
A caution sign remains posted at Gibbs Lake south of Port Townsend as well as at Lake Leland, north of Quilcene, and Crocker Lake because the lakes contain the types of algae known to at times begin to produce poisons.
No toxins were detected in Lake Leland, which has a medium bloom, with some scum near the dock.
No sample was taken from Crocker Lake, which is near the U.S. Highway 101-state Highway 104 junction.
The lake has a light bloom.
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 http://tinyurl.com/6z64ofy.
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Managing Editor/News Leah Leach can be reached at 360-417-3531 or at leah.leach@peninsuladailynews.com.