That is because a volunteer for the Surface Water Management Division earlier this week found high levels of the toxin microcystin, which can damage the liver, said Marisa Burghdoff, water quality specialist for Snohomish County.
The toxin is produced by cyanobacteria, commonly known as blue green algae or toxic algae. It looks like green paint floating on the surface.
Lake Howard is 26 acres in size and located in the Seven Lakes area, north of the Tulalip Reservation.
The department installed signs and sent emails to residents warning them to avoid swimming or boating in parts where large concentrations of algae scum can be found. Pets and livestock also can be in danger if they drink the water.
People or their pets exposed to the algae must seek medical attention if they have symptoms of poisoning or unexplained sickness.
A small amount of the algae in lakes is normal, but it does not always produce the toxin. The county plans to do testing every week until the levels decrease, Burghdoff said.
The algae grows in response to high levels of phosphorus. Phosphorus mainly increases because of poorly maintained septic systems and pollution by fertilizers, pet waste and erosion sediments running into the water.
A campaign to reduce pollution in the lake is planned in August, she said.
High levels of algae was found last year from the end of September to November, Burghdoff said.
The algae also was detected in Lake Stevens in June, but the toxin was not found in high levels.
For more information, people can visit www.lakes.surfacewater.info.
Alejandro Dominguez: 425-339-3422; firstname.lastname@example.org.
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