LAKE STEVENS — The city’s third annual treatment to manage algae in its namesake lake is scheduled to start Monday.
It’s a $100,000-a-year project meant to prevent the bloom of potentially toxic algae.
The city in 2013 began treating the water once a year with aluminum sulfate, a chemical compound that eliminates excess phosphorus in the water. Algae feeds on phosphorus, so high levels of it can lead to a rapidly growing problem.
Most of the algae in the lake shows up as an unappealing but nontoxic green and brown mat that floats on the surface. However, areas of toxic blue-green algae have been found in the water, most recently in January. Though the concentration of toxic algae is not considered dangerous to swimmers and boaters, it can poison dogs or other animals that drink from the lake.
The city has a formal plan, adopted in 2013, to manage phosphorus levels and thus control the algae.
“If we can get the excess phosphorus out of the lake, the lake will balance itself,” public works director Mick Monken said. “You’ve got to have some phosphorus in the water, but when you have too much of it, it not only feeds the good stuff, it also feeds the bad stuff.”
The lake’s overload of phosphorus — an element found in soil and most living things — is caused by fertilizers, runoff from buildings and roads, erosion from clearing land, leaking septic systems, and waste from wild animals, pets and livestock.
The city pays 89 percent of the cost for the annual treatment — about $89,000 — while the county covers the other 11 percent. By 2020, the city and county estimate they will have spent a total of $700,000 on controlling algae in the lake, according to the phosphorus management plan.
This year’s treatment is scheduled to start Monday and wrap up March 14. There are no restrictions for recreation in the lake during the week.
People may notice that the water seems to change color, gaining an almost tropical turquoise hue during the treatment, Monken said. The water itself isn’t changing, but the aluminum sulfate forms clouds as it settles toward the bottom of the lake and the light bounces off those clouds, creating the illusion of brighter, shallower water.
“If we had white sand underneath, that’s what the lake would look like all the time,” Monken said.
Next week’s treatment to manage algae is separate from the city’s ongoing battle with milfoil, an aquatic weed that has taken over much of the lake in past years. The city has budgeted $45,000 this year to remove milfoil.
Kari Bray: 425-339-3439, kbray@heraldnet.com
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