The city's environmental programs manager told council on July 15 that Lake Stevens participated in a U.S. Environmental Protection Agency study of perchlorate levels in lakes before and after July 4 fireworks events and that the 2024 sampling showed a temporary increase at North Cove Park that exceeded an ecological screening value.

Why it matters: perchlorate (prechlorate in staff remarks) is used in fireworks and can affect thyroid function in humans and wildlife; the city's testing aims to determine whether large public fireworks events measurably change perchlorate concentrations and whether those changes pose local risks.

Shannon (Environmental Programs Manager) summarized the 2024 participation in the EPA study of 226 lakes, which sampled before, the day after, and a week after fireworks. The city's 2024 results showed a spike at North Cove Park on the day after the event (July 5) with concentrations above a line the study used at roughly 1 part per billion as a level where aquatic effects have been observed; a week later levels returned toward baseline. Shannon said the Washington EPA/California guidance the city reviewed set higher human‑health thresholds (the California human-health level cited during the meeting was about 6 ppb) and that Lake Stevens is not used as a drinking-water source. Shannon told council: “we did see an increase in the precorite levels specifically at North Cove Park. The day following the fireworks ... and then a week later that those levels came back down.”

Council asked about human health, fish bioaccumulation and possible interactions with lake management (alum treatments, milfoil). Shannon replied the available literature she reviewed did not indicate strong bioaccumulation in fish but that tissue sampling would be required to assess fish exposure; she said human-health thresholds cited by some regulators are notably higher than the short-term spikes observed in the lake and that the city will await 2025 results to see if a repeated pattern emerges. Councilmembers also asked about air-quality impacts from fireworks; Shannon said the city does not currently operate local air sensors and suggested staff could research literature and external air-quality monitoring (Puget Sound Clean Air Agency) to supplement water sampling.

Next steps: the city repeated sampling for the July 4, 2025 event and is awaiting lab results. Staff recommended continuing monitoring and possibly adding sediment or fish-tissue testing or coordinating air-quality monitoring if council directs further study.