This new sign has been posted recently in several locations around the park. (Washington State Parks)

CHIMACUM — A deadly nerve toxin created by blue-green algae in Anderson Lake has exploded in one week from more than nine times the recreational threshold to nearly 5,000 times the allowable amount of 1 microgram per liter.

Samples taken Monday found the level of anatoxin-a to be 4,933 micrograms per liter, the Jefferson County Public Health Department announced Friday after test results were received.

That is a huge increase from the amount found in a May 6 sample.

As soon as test results on May 9 showed that the sample contained 9.35 micrograms per liter of anatoxin-a, which can cause illness and death in humans and animals within four minutes of being ingested, State Parks — upon the advice of the county health department, which does the testing of the lake — closed the lake to all recreation, including fishing, boating and swimming.

The toxin level in Monday’s sample “is the second highest toxin level measured at Anderson Lake” since testing began after two dogs died of drinking lake water on Memorial Day weekend in 2006, said Michael Dawson, water quality manager for Jefferson County Public Health, in the press release.

Just the day before the latest sample was taken — when the toxin level was undoubtedly high — a dog died after briefly splashing in the lake.

Clue, an Australian kelpie less than 2 years old, “got in at one point up to its chest for no more than 30 seconds,” said Mike Moore of Poulsbo, whose 20-year-old daughter owned the recently adopted dog.

“The dog either fell in or waded its way in, and my daughter pulled it back out because it was on a leash.”

That happened at about 11:30 a.m. Mothers Day. At 2:30 p.m. that day, Clue was euthanized by a Silverdale veterinarian, the family said.

No official report was made to Jefferson County or State Parks, Dawson said.

State Parks had posted on May 9 red signs that read: “Danger. Lake Closed due to toxic algae. Keep Out Of Lake” as has been done each time the lake has been closed because of toxic algae. Rangers also had hung yellow caution tape at the boat launch.

As has happened since the nearly annual closures of the lake because of toxic algae over the past decade, the rest of the 410-acre Anderson Lake State Park between Port Townsend and Chimacum remained — and still remains — open to hiking, bicycling, horseback riding and other recreation.

Moore has said in a variety of media reports that signage was insufficient for his family to be warned of a danger at the lake, so State Parks has prepared signage that offers more details, said Jay Carmony, southwest regional assistant manager for Washington State Parks, on Friday.

The new signs, which he said have recently have been posted around the lake, read: “Danger. Toxic. Lake Closed. Stay Out of Water. No Pets in Lake. Exposure to water in this lake will cause serious injury or death for people and animals.”

The signs also have symbols representing prohibition of animals in the lake and swimming.

The number of signs posted also has been increased, Carmony said. Signs have been placed at areas that some may use as informal entrances to the park, in case visitors bypass the signage at the formal entrance.

If the Moore family “accessed the property from somewhere else” than the formal entrance “then we don’t know what signage they would have encountered,” Carmony said.

“Our hearts go out to the family,” Carmony said. “It’s very unfortunate.”

Locals are very aware of the varying status of the lake, but tourists may not be as informed, Carmony said.

“We want people to be as safe as possible,” he said.

Many enjoyed fishing in Anderson Lake this winter, according to Dawson, and testing, which resumed in April after the last of the season was done in November, found low levels of anatoxin-a in the lake on April 29.

Since then, however, the toxin level has continued to grow, and has skyrocketed recently.

“That’s the definition of an algae bloom,” Dawson said. “It grows exponentially.”

The toxin is created by blue-green algae, a natural occurrence that at times produces poisons. Researchers do not know what prompts the release of the toxin, but they do know that warm weather encourages algae growth and thus the possibility of toxins in the water.

Nutrients such as phosphorus and nitrogen also feed algae growth.

In 2008, it was reported that Anderson Lake had set a worldwide record for the highest levels of anatoxin-a ever recorded, hitting 172,640 micrograms per liter.

Dawson said Friday that the testing method has changed since then.

“With the method we use now, you can’t directly compare the numbers,” Dawson said.

“Under modern testing regime, other lakes are higher than ours now.” Among them are a lake in Thurston County and one in Island County, he said.

Dawson said that officials now are working with a lake specialist on management plan to “identify if there are feasible options for controlling the algae.”

In the meantime, “the main message we are trying to get across is that lake toxins are very dangerous to both humans and animals.

“When in doubt, stay out.”

Toxins have not been found in Clallam County lakes.

To check on lake status in Jefferson County, see https://tinyurl.com/PDN-jeffcolakestatus.

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Executive Editor Leah Leach can be reached at 360-417-3530 or at [email protected].

A sandwich board with the red sign and yellow caution tape were placed at the park after the Jefferson County Public Health Department told Washington State Parks that toxin levels surpassed the recreational limit for exposure. (Washington State Parks)