The waters of Blackman Lake as seen on a cloudy day in July.
SNOHOMISH — The city will use alum treatments to help control toxic algae blooms at Blackman Lake.
The City Council signed off on the plan last week.
Nearly $500,000 in funding is expected to be earmarked for the lake treatments in the proposed 2025-2026 biennial city budget which comes out this fall.
The plan also calls for investigating modern underwater oxygen pumps as a future non-chemical option for the lake.
Studies found phosphorous in the lakebed is helping create conditions where blue-green algae thrive.
Aluminum sulfate (alum) treatments lock in phosphorous to the bottom of the lake.
Alum treatment will cost approximately $460,000 for the permitting, application, monitoring and more.
An alternative to alum is lanthanum, a treatment made from clay. It’s sold as EutroSorb.
The estimated annual cost for alum treatments is $50,000 or $125,000 a year whether applying two treatments a year or quarterly treatments annually.
The plan is posted to the city’s Blackman Lake Cyanobacteria Management Plan web page, www.snohomishwa.gov/808/Blackmans-Lake-Management
