The level of a liver toxin created by blue-green algae in Gibbs Lake has dropped below the danger level.
However, a warning sign will remain posted at the lake south of Port Townsend for at least one more week, said Greg Thomason, Jefferson County environmental health specialist, last week.
“If it is below the warning level next week, then we will take down the warning sign,” he said, adding that caution signs would remain posted because the lake contains algae that are known to produce toxins.
The most recent test of a sample of water from Gibbs Lake found that microcystin, a liver poison, had dropped to a level of 3.6 micrograms per liter.
The recreational safety threshold for microcystin, which can damage the liver after longtime ingestion, is 6 micrograms per liter.
Preliminary test results the previous week had found 6.8 micrograms per liter of microcystin in Gibbs Lake.
That had prompted the posting of warning signs recommending that no one swim in the water or drink it and that pets and livestock be kept away.
Fishing is permitted in a lake posted with a warning sign, but fish should be well-cleaned with the guts discarded.
A caution sign carries the similar recommendations, but permits swimming as long as swimmers avoid algae scums.
“We’re keeping our fingers crossed” that the level will remain low in Gibbs Lake, Thomason said.
The other toxin typically found in East Jefferson County lakes, anatoxin-a, remained below detectable levels in the latest sample from Gibbs Lake.
Anatoxin-a is a fast-acting nerve poison that can be fatal.
Toxin levels at Anderson Lake — historically the worst in the county for high levels of anatoxin-a — remain low, but are creeping up, Thomason said.
The latest test found 0.82 micrograms of anatoxin-a per liter in Anderson Lake.
The recreational safety threshold for anatoxin-a is 1 microgram per liter.
“It’s been coming up about two-tenths of a microgram per liter every week for about five weeks,” Thomason said. “We’re hoping the cloudy weather and cooler weather will slow it down.”
Microcystin was at 0.18 per liter.
Anderson Lake remains open to fishing and other recreation but is posted with a “caution” sign because of the existence of some toxins in the water.
The lake near Chimacum, which is in Anderson Lake State Park, was reopened Aug. 27 after having been closed since June 10 because of high levels of anatoxin-a.
Anderson Lake State Park, which is around the lake, has never been closed to recreation.
Tests found no detectable levels of either toxin in Lake Leland north of Quilcene. Caution signs remain posted there because the lake contain algae that are known to produce toxins.
Silent Lake on the Toandos Peninsula is posted with a caution sign.
Sandy Shore Lake south of Port Ludlow remains clear.
Blue-green algae growth is thought to be encouraged by warm, sunny weather when sufficient nutrients, such as phosphates, are present.
But researchers don’t understand why some species of blue-green algae will begin to produce toxins, nor what fuels increases in the amount of toxins.
Shallow, aging lakes are more likely to become overgrown with algae and contain toxins.
Clallam County lakes, most of which are deep and relatively free of algae, are not tested for toxins.
To report algae blooms in Clallam County, phone 360-417-2258.
Information about Jefferson County lake quality is posted at http://tinyurl.com/6z64ofy.
To report blooms in Jefferson County, phone 360-385-9444.
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Managing Editor/News Leah Leach can be reached at 360-417-3531 or leah.leach@peninsula
dailynews.com.
