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Blackmans Lake Management
Blackmans Lake Alum Treatment Update
An alum treatment at Blackmans Lake is scheduled to begin on Friday, March 28th, 2025, with preparation and equipment setup taking place on Thursday, March 27th at Ferguson Park. The treatment is expected to take approximately six days, including weekend work, and will be monitored by environmental consultant staff.
The project is anticipated to be completed by Wednesday, April 2nd, with demobilization and any necessary site restoration occurring on Thursday, April 3rd.
Updates will be provided if there are any changes to the schedule.
The Blackmans Lake Cyanobacteria Management Plan is a strategic approach to address and manage cyanobacteria-related issues at Blackmans Lake, aimed at preserving water quality and ecosystem health.
Blackmans Lake has experienced blue-green algae blooms over the past years. Blue green algae is capable of producing toxins which can cause serious illness in people and pets that come into contact with affected water. The blue-green algae bloom looks like blue or green paint floating on the surface. Signs are posted at the parks and a notification is posted on the City website when a blue-green algae bloom is identified at Blackmans Lake. Lake users should avoid contact with the water and keep pets away from the lake when it is experiencing a blue-green algae bloom.
In 2022, the City Council authorized a contract with Herrera Environmental Consultants, Inc. (Herrera) to complete the Blackmans Lake Cyanobacteria Management Plan (Plan) to address blue green algae. In 2022 and 2023, Herrera coordinated water sampling with volunteers, Snohomish County Lakes Division, and the City at Blackmans Lake as part of the Plan. On May 20, 2024, Herrera presented their findings and recommendations to address the blue-green algae blooms based on site visits, and the analysis and review of the data from the Blackmans Lake water samples.
Below are links to the May 20, 2024, presentation slides and Quality Assurance Project Plan.
Herrera presented the draft plan to Council on July 16, 2024. The presentation included a discussion on the data analysis and recommendations.
The final plan was adopted by Council on August 20, 2024. The final plan is linked below.
City Council authorized a contract with SOLitude Lake Management on February 18, 2025 to implement the Blackmans Lake 2025 Alum Treatment. Permit application has been submitted to the Department of Ecology for review and approval. It is anticipated that the treatment will occur in the spring. Schedule is dependent on permit approval. Please see link below for the Council staff report that begins on page 39.
Please send questions to Yoshihiro Monzaki, City Engineer at monzaki@snohomishwa.gov.