Watershed Health and Lake Stevens

The health of the Lake Stevens watershed directly affects the lake’s water quality. Activities throughout the watershed can introduce pollutants into the lake through stormwater runoff. The City helps protect the lake through the following lake management programs:

Stormwater Maintenance

• Stormwater system care – Regular cleaning of catch basins and storm drains to prevent debris and pollution from entering the lake.
• Street sweeping – Removes dirt, oil, and litter from roadways before it washes into the storm system.
• Facility inspections – Ensures stormwater ponds and treatment systems are functioning properly.
• Public outreach – Educates residents on how daily actions affect lake health (e.g., proper fertilizer use, pet waste disposal).

Lake Level Monitoring

The lake level is managed with an outflow control structure called a weir that regulates the amount of water leaving the lake. This structure is operational in the spring and summer to raise the lake level for the summer months for recreation when rainfall is limited. In the fall, the structure is removed, and the water is free-flowing through the Outlet Channel. Removing the structure in the fall lowers the lake level and creates storage in the lake for rainfall in the wet season. 

The lake level is monitored with a water level data logger along with a physical staff gauge mounted in the North Cove area of the lake. The City collects the data from the logger once per week throughout the year as well as collecting a visual reading from the staff gauge. This information is recorded along with the current elevation setting of the weir. This information is critical during the early spring and late fall months when the weir will often need to be adjusted to lower the lake levels to handle anticipated rainfall events. Historic lake level data is available here:
Click the button below to explore historic lake-level data in an interactive dashboard.
 VIEW HISTORIC LAKE-LEVEL DASHBOARD

Aquatic Plant and Algae Management Plan

Aquatic plant management in Lake Stevens is focused on maintaining a balance between preserving the lake’s natural ecosystem and ensuring it remains safe and accessible for recreation. While native aquatic plants are important for fish habitat and water quality, invasive species—like Eurasian watermilfoil—can grow rapidly and disrupt these functions. The City monitors plant growth regularly and uses targeted methods such selective herbicide application to control invasive species while minimizing impacts on native vegetation. Public education also plays a role, with efforts to prevent the spread of invasive plants through responsible boating and lake use.

Phosphorus management in Lake Stevens focuses on reducing nutrient levels to prevent harmful algal blooms and protect water quality. The City of Lake Stevens, in partnership with Snohomish County, applies aluminum sulfate (alum) treatments annually to bind phosphorus in the lake’s water and sediments. This approach has replaced a less effective aeration system retired in 2012. In addition to in-lake treatments, community outreach through the “I Love Lake” campaign encourages residents to reduce phosphorus runoff by maintaining septic systems, limiting fertilizer use, and managing pet waste. Ongoing monitoring and public involvement are key to maintaining a healthy lake ecosystem.

For information regarding aquatic plant and algae treatment, please visit Lake Stevens Noxious Aquatic Weed and Phosphorus Management Program.