PORT TOWNSEND — The level of a fast-acting nerve poison is down in Anderson Lake, but the water remains deadly.
The level of anatoxin-a dropped to 166 micrograms per liter last week, according to test results received Friday.
That’s a big drop from the prior week’s measurement of 534 micrograms per liter — the highest seen in the lake this season — but still way above the warning level of 1 microgram per liter, said Greg Thomason, Jefferson County environmental health specialist, on Friday.
“So the lake stays closed,” he said.
Anderson Lake, a popular trout-fishing lake between Port Townsend and Chimacum, was closed May 3 because of elevated levels of toxins in the water.
The 410-acre state park surrounding it stays open to the public. A Discover Pass is needed to park there.
Toxins are created by blue-green algae, which is generally benign, but some species can begin to produce toxins at times.
A heavy bloom and scum around the edge of the lake can be seen.
No microcystin — a toxin that can cause skin irritation and, if ingested over a period of many years, can result in liver failure — was found in Anderson Lake, Thomason said.
The week before, the level was 1.4 micrograms per liter, which was far below the safety threshold of 6 micrograms per liter.
Other lakes
Levels of algae-produced toxins also fell in Leland and Gibbs lakes, the other two tested last week.
Both have tested below safety thresholds throughout the summer.
The level of anatoxin-a dropped to 0.06 last week from 0.52 the week before at Leland, which is north of Quilcene.
No microcystin was found.
No anatoxin-a was found in Gibbs Lake, north of Port Townsend, and microcystin was down to 0.05 from 0.11.
Caution signs remain posted at both Leland and Gibbs lakes because they contain algae known to sometimes suddenly begin to produce toxins.
“The toxin-producing algae is the dominant algae in Leland, so anything can happen,” Thomason said.
He warned that since test results of samples taken Mondays are issued Fridays, they are always several days behind the actual condition of the lakes, and the level of toxins can change quickly.
A caution sign remains at Crocker Lake because it, too, contains algae known to produce toxins.
The dip in toxins is probably because of cooler, cloudier weather, Thomason said.
“Cooler weather, little less sunlight will slow it down,” he said.
Sunny weather and warm temperatures encourage the growth of blue-green algae when sufficient nutrients, such as phosphates, are present.
It also could be that samples were taken during a period of less activity.
‘Come and go’
“These blooms come and go,” he said.
“They last an average of five to eight days, then another comes in.”
Higher levels could be the result of many blooms overlapping each other, he said, while a decrease could be because the sample was taken during a die-off or in between blooms.
“We just happen to get in there once a week. Sometimes we’re at a peak, sometimes at a trough,” Thomason said.
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.
A Discover Pass — which is $10 for one day or $30 for an annual pass, and which can be purchased at state parks — is needed to visit state parks.
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.