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City briefs council on Lake Stevens health, monitoring and treatment options
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Summary
City environmental staff told council that Lake Stevens is in generally good health, described monthly monitoring and treatment programs (alum treatments cost about $150,000–$200,000), and reported small, short‑term spikes in perchlorate after fireworks that remain below EPA drinking‑water levels.
City environmental staff delivered an extensive briefing Feb. 24 on Lake Stevens’ water quality, monitoring programs, and management tools.
Shannon Front, the city’s environmental programs manager, explained that the lake is roughly 1,000 acres with a watershed of about 3,500 acres and that phosphorus—more than nitrogen—is the principal nutrient driving algae blooms there. Front described two categories of phosphorus input: external loading (runoff, septic systems, pet waste, fertilizers) and internal loading (phosphorus stored in lake sediments that can be remobilized under low oxygen conditions).
Front reviewed historical treatments: an aerator operated from 1994 to 2012 and alum treatments in place since 2013. She said a sediment study in 2021 showed alum remains effective; as a result the city treats on an as‑needed basis—typically every two to four years depending on monitoring. She estimated an alum treatment runs roughly $150,000–$200,000 and requires a contractor under the city’s NPDES permit.
On monitoring and response, Front described monthly sampling (Secchi disk clarity, phosphorus and chlorophyll measurements) and a protocol to collect samples and send them to the King County lab; that testing generally takes one to two days. "When in doubt, stay out," she said, explaining the city posts signs and notifies lakefront homeowners and public swim groups when scums or suspected blooms are observed.
Front also summarized recent sampling for perchlorate (a compound associated with fireworks). Staff found small spikes immediately after July 4 that returned to background levels within a week and remained below EPA drinking‑water thresholds; staff said long‑term sampling every three to four years would be useful but is not currently budgeted.
Council questions focused on treatment costs, turnaround time for lab results, the drivers of historical phosphorus trends, and the city’s monitoring capacity; staff said the stormwater utility and lake‑benefit fees fund the program and a rate study is planned to evaluate long‑term revenue sufficiency.
Next steps: staff will continue monthly monitoring, pursue permits and contractor selection for treatments when needed, and return with the results of an upcoming rate study and any recommendations about sampling frequency for perchlorate.
