Anderson Lake was closed to fishing, boating and swimming Friday, a little more than a week before it would have been closed for the season.
The level of a fast-acting nerve toxin shot up, according to the latest results of tests of water samples from the lake, said Greg Thomason, Jefferson County environmental health specialist.
The toxin, anatoxin-a, was recorded at a level of 6.58 micrograms per liter. The recreational safety threshold for anatoxin-a is 1 microgram per liter.
Thomason recommended to Mike Zimmerman, Anderson Lake State Park manager, that the lake be either posted with a warning sign or closed.
“At this time, it’s probably best to close it rather than put up a warning sign,” said Zimmerman, “since the park itself closes for the season on the first of November.
“We don’t want to have to continue to change the signage on the lake,” he added.
Anderson Lake, which is within a state park near Chimacum, was the only lake sampled in East Jefferson County last week that showed a level of algae-created toxin — either anatoxin-a or the liver toxin microcystin — above safe levels, Thomason said.
This is the second closure of the lake prompted by toxins this year.
Anderson Lake had been 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.
Toxins are created by certain species of blue-green algae. The growth of the algae is thought to be fueled 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 drives increases in the amount of toxins.
The resurgence of toxins this late in the year was a surprise.
“This is the latest we’ve seen anatoxin-a come back,” Thomason said.
The cause is open to speculation.
When King County Environmental Labs returned the results of water samples, it noted that the area has experienced a warm fall with a lot of sunny days, Thomason said.
That “probably accounts for the algae doing their thing a little later than normal,” he said.
Anatoxin-a, a neurotoxin that acts quickly and that can be fatal, was also found in high levels — in the hundreds of micrograms per liter — in Kitsap Lake in Bremerton and Lake Spokane, Thomason said.
“Anderson was not the only one,” he said.
“There’s been a late bloom of algae around Seattle.”
Although the levels of both anatoxin-a and microcystin, a slower-acting liver toxin, were below the safety threshold in Leland, Gibbs and Crocker lakes, caution signs remain posted at all three lakes because of algae blooms.
The algae bloom is especially heavy at Crocker Lake, which is off U.S. Highway 101 near the intersection with state Highway 104.
“It’s as heavy a bloom as anything we’ve seen in Anderson,” Thomason said.
“This is the first time we’ve seen this kind of bloom in Crocker.”
Gibbs Lake south of Port Townsend also contains a heavy bloom, while that at Lake Leland north of Quilcene is lighter.
Overall, “it’s been a bad year for toxic algae blooms,” Thomason said.
“They’re hanging on late for some reason.”
Anderson Lake won’t be monitored again until late March or early April, Zimmerman said.
After the winter closure that begins Nov. 1, the lake is expected to be reopened at the beginning of the fishing season the last Saturday of April — if toxin levels are below the safety threshold.
Information about Jefferson County lake quality is posted at http://tinyurl.com/6z64ofy.
To report blooms in Jefferson County, phone 360-385-9444.
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.
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Managing Editor/News Leah Leach can be reached at 360-417-3531 or leah.leach@peninsuladailynews.com.