Lake Management


Alum treatment notice

The City of Lake Stevens and Snohomish County perform annual alum treatments on Lake Stevens to control phosphorus. Lake Stevens will be treated with alum annually in the fall. The applicator will post signs in the treated and potentially affected areas no more than 48 hours prior to treatment. The signs will describe any water use restrictions or advisories.

If you want additional notification prior to treatment, or have further questions, please contact Shannon Farrant at or (425) 622-9442. This treatment is regulated by a permit through the Washington State Department of Ecology

Lake Stevens Eurasian Milfoil Management

Lake Stevens wouldn’t be Lake Stevens without the lake. And because of that, we're taking steps to ensure that the lake is here for many generations to come. Two of those steps are managing the Eurasian Milfoil (invasive species) and algae (natural occurrence).

Our partner in milfoil management, Aquatechnex,  is a fully integrated lake and aquatic plant management firm that operates primarily in the Western and Upper Midwest states. Their team evaluates the Eurasian Milfoil growth present in Lake Stevens and sets the treatment date and locations.

The following link will connect to Aquatechnex's Lake Stevens treatment page:  

Algae Management

June 2012 algae bloomThe City of Lake Stevens and Snohomish County have developed a Phosphorus Management Plan to address how we plan to control high nutrient (phosphorus) loadings in Lake Stevens which can result in unwanted algae growth. The current treatment is to use Alum to reduce the phosphorus levels back to naturally occurring levels. Tetra Tech, in conjunction with the City and County, prepared a technical memorandum that discusses sources of internal and external phosphorus sources and what naturally occurring levels may look like. The report can be viewed at this link.

Algae blooms are a natural occurrence in Lake Stevens and is important to the productivity of Lake Stevens' eco-system. Algae is part of the food chain that feeds small life forms that in turn provide a food source for fish and so on up the food  chain, meaning most algae are desirable for lakes. Some algae, such as filamentous green algae and blue-green algae, are 
not desirable and are of concern for Lake Stevens.

Both of these types of algae thrive in a nutrient-rich lake. The Filamentous green algae, while generally harmless, can interfere with boater access, recreation, and aesthetics. This type of algae produces thick mats on the water's surface. Blue-green algae are actually bacteria and are of greater concern than true algae because some species can produce potent toxins. While not all blue-green algae is toxic, it is best for people and pets to avoid contact with surface sums whenever a blue-green bloom is suspected.

The City will be conducting a sediment study in 2021 that will be used to update the current Phosphorus Management Plan.