CHIMACUM — Anderson Lake is open for fishing — but with a warning.
Tests on two consecutive samples taken from the lake — on Nov. 13 and Nov. 26 — found that toxins had declined to safe levels, Jefferson County Public Health announced Thursday.
However, that could change in the coming weeks or months, said a public health official, and no more testing will be done until April.
“It may change,” said Tim Weissman, county environmental health specialist. “We could have a spell of really warm weather in March. We could have a bloom come back and we won’t necessarily know about it.”
So the county recommended, and the Anderson Lake State Park officials agreed, to replace the closure signs that have been up at the lake since early June with warning signs.
Warning signs, which are a step more cautionary than caution signs, say that toxins are at or above state guidelines or that there is an extensive bloom dominated by toxic species.
That isn’t the case at this point.
Concentrations of anatoxin-a — a fast-acting and possibly deadly nerve poison — were found to be 0.168 and 0.129 micrograms per liter, respectively in the two tests. Both of those samples tested below the 1 microgram per liter recreational guideline set by the state Department of Health.
The other blue-green algae toxin historically found in Anderson Lake, the slower-acting liver toxin microcystin, was found in the Nov. 13 sample at concentrations below the recreational guideline of 6 micrograms per liter and it was not detected at all in the Nov. 26 sample.
But given the history of Anderson Lake, it was thought best to err on the side of caution, Weissman said.
Routine testing of the lake began in 2007 after two dogs died in 2006 after drinking Anderson Lake water.
Since then, the lake has been forced to close every year due to toxins, sometimes for much of the year. For instance, late season blooms kept the lake closed through fall 2017 but early 2018 saw five consecutive months of open access.
In 2008, the lake set a worldwide record for the highest levels of anatoxin-a ever recorded, hitting 172,640 micrograms per liter.
The most recent algae bloom has only recently dissipated and could return, Wiessman said. He also pointed out that researchers did spot sampling, which may not represent all of the lake.
“We know that there is toxic algae in Anderson. It’s just at low levels,” he said Thursday.
Blue-green algae, like that found in Anderson Lake, are naturally occurring and found in freshwater lakes across the state. However, sometimes these blooms produce toxins that are released into the water, though why this happens isn’t fully understood.
Hot weather tends to encourage the growth of algae and thus poses the greatest risk of toxins forming.
In 2016, the state Department of Fish & Wildlife extended the fishing season at the lake between Port Townsend and Chimacum to year-round to allow recreational fishing during the colder months when blooms are less likely to occur.
Those who fish in the lake, once renowned for its trout, are urged to use the lake at their own risk; to avoid contact with areas of scum, or water that is green in color; to keep children and pets out of the water; and to clean fish well and discard the guts since some algae toxins are known to accumulate in fish tissue.
The 410-acre Anderson Lake State Park remains open to hiking, bicycling, horseback riding and other recreation.
To check the status of Jefferson County Lakes, go to jeffersoncountypublichealth.org/723/Lake-Status or call 360-385-9444.
For fishing seasons and regulations see the state Department of Fish and Wildlife website www.wdfw.wa.gov/fishing.
Information on Anderson Lake State Park is available at www.parks.state.wa.us/240/Anderson-Lake.
