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Bremerton treats Kitsap Lake to tackle toxic algae

caption: Toxic algae covers the surface of Lake Kitsap in Bremerton in 2019.
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Toxic algae covers the surface of Lake Kitsap in Bremerton in 2019.
City of Bremerton

Ever heard of lanthanum? The metallic element is a fairly obscure one, number 54 on the periodic table of the elements, soft enough to cut with a knife.

Some kidney patients take chewable tablets of lanthanum to lower levels of phosphate in their blood.

The city of Bremerton plans to use a powdered form of lanthanum on Monday and Tuesday to lower levels of phosphorus in the city’s only lake, Kitsap Lake.

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The plan is for contractors on a barge to stir lake water and a lanthanum-clay mixture in a vat, then spray the liquid both onto the lake surface and below it. The lanthanum bonds with phosphorus in the lake and turns it into a mineral, making the phosphorus unavailable for toxic algae to use as a nutrient.

“Algae grows very well in a nutrient-rich environment,” said Chance Berthiaume with Bremerton Public Works and Utilities.

Harmful algae blooms have become a problem in lakes and saltwater bodies around the country.

A 2023 study of 2,800 lakes in the United States in the journal Nature Water found that a warming climate is boosting the production of algae toxins, with the highest levels in water temperatures between 68 and 77 degrees Fahrenheit.

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Decades of polluted runoff containing phosphorus and nitrogen essentially fertilized Kitsap Lake and fueled its boom in toxic algae. The City of Bremerton found that a buildup of phosphorus in the 248-acre lake’s sediment was the main driver of Kitsap Lake’s toxic cyanobacteria, also known as blue-green algae, as well as aggressive vegetation growth.

Between algae blooms and E. coli bacteria outbreaks, the lake had to be closed to public use about 80% of each summer, Berthiaume said.

In September 2019, a police dog had to be treated for exposure to algal toxins after it chased a suspect into the lake, according to EutroPHIX, one of the companies treating Kitsap Lake.

“Algal blooms are often related to excess nutrients such as phosphorus, so people can help prevent them by being careful to apply only the fertilizer that their lawns and gardens need and practicing other lake-friendly gardening techniques,” Washington Department of Ecology spokesperson Scarlet Tang said in an email.

In 2020, Bremerton started treating Kitsap Lake with a lanthanum product. Berthiaume said phosphorus levels in the lake’s depths have dropped 90%, and the lake has had no summer algae blooms since.

“It’s pretty phenomenal, the results we’ve achieved,” he said. “The use of the lake has gone through the roof.”

RELATED: Is that toxic algae? Washington officials warn: 'When in doubt, stay out.'

Long Lake in Thurston County also was treated with lanthanum in May, while Lacamas Lake in Clark County and Moses Lake in Grant County are scheduled for treatment in 2024.

The City of Bremerton is paying Bellingham-based Aquatechnex $525,000 for three years of lanthanum treatments.

While lanthanum treats the symptoms, not the causes, of lake pollution, Berthiaume said the city will install stormwater treatment facilities around the lake in 2024 and 2025 to remove lake-harming nutrients before they can enter Lake Kitsap.

Not all algae blooms are harmful. But, state health officials say, if you see discolored or slime-covered water and don’t know what’s causing it: "When in doubt, stay out!"

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