PORT TOWNSEND — The level of a potentially deadly nerve toxin has climbed to unsafe levels again in Anderson Lake after a couple of weeks of low readings.
The Jefferson County Public Health Department on Friday recommended that the popular trout-fishing lake west of Chimacum stay closed to all recreational use.
The level of anatoxin-a, a fast-acting nerve poison that can cause paralysis and stop breathing, had been below the safety threshold in two consecutive weekly tests earlier this month.
That led county health officials to recommend that the lake, which was closed for most of the summer because of elevated levels of anatoxin-a, be reopened.
But Mike Zimmerman, the ranger in charge of the lake at the Anderson Lake State Park, declined to reopen the lake so late in the season, which ends Oct. 30.
Zimmerman said at the time that, given warm weather that would fuel plant growth, he didn’t trust that the level of toxin created by blue-green algae would stay low.
It turned out he was right, according to the report received Friday from King County Environmental Labs, which found that a sample of water from the lake contained 1.43 micrograms of anatoxin-a per liter of water.
That’s slightly above the safety threshold of 1 microgram per liter.
“Anderson Lake jumped up above the warning level,” said Greg Thomason, Jefferson County environmental health specialist.
“We’re now recommending that it stay closed.”
The lake may look healthy, with only a light bloom and no scum, “but you can’t tell by looking at it,” Thomason said.
The 410-acre Anderson Lake State Park around the lake remains open for recreation until the end of October. A Discover Pass is needed to park there.
Microcystin, another toxin created by blue-green algae, stayed low in Anderson Lake, as it has all season, with the sample containing only 0.30 micrograms per liter of water.
The safety threshold is 6 micrograms per liter for microcystin, which can cause skin irritation and nausea over the short term and liver damage if ingested over a long period of time.
Microcystin remained low in Gibbs Lake in the tests.
Gibbs Lake was reopened Sept. 7 after two consecutive weeks of low readings for microcystin.
The lake south of Port Townsend had been closed Aug. 23 because tests of a sample from the lake found 19.4 micrograms of microcystin per liter of water.
Since it was reopened, its status has been upgraded from a warning level to a caution level.
The caution sign is posted at the lake only because the water contains the type of blue-green algae known to sometimes create toxins.
For the same reason, caution signs remain at Lake Leland north of Quilcene and at Crocker Lake, which is near the U.S. Highway 101-state Highway 104 junction.
Tests of Lake Leland water samples last week found no anatoxin-a or microcystin.
Crocker Lake was not tested last week.
Blue-green algae is a plant that grows naturally in lakes, especially shallow, older bodies of water.
At times, some species of blue-green algae produces toxins.
Although researchers know that algae growth spikes in the summer when sufficient nutrients such as phosphates are present, they don’t understand what sparks the production of toxins from some species.
Testing of East Jefferson County lakes will continue through September, Thomason has 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.
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.
