Aquatic plant survey summary

Lake Stevens has a history of invasive aquatic plants, particularly Eurasian Milfoil, which heavily impacted the lake in the late 2000s. The City launched a treatment program in 2011, successfully reducing its presence. Over time, native Largeleaf Pondweed has reestablished in the lake, benefiting wildlife but affecting some of the recreational use. More recently, Curly Leaf Pondweed was detected in small areas, prompting continued monitoring and treatment efforts.

On May 28th, biologists conducted a survey using GPS to map invasive and nuisance plants. The primary treatment targets are Eurasian Milfoil and Curly Leaf Pondweed, with secondary focus on dense native species affecting beneficial lake uses.

The first treatment plan includes applying ProcellaCOR herbicide to 19.19 acres of Eurasian Milfoil and Galleon herbicide to 4.74 acres of Curly Leaf Pondweed. There are no water use restrictions for these treatments except for a short window for drawing water for irrigation. These treatment are also not subject to the Department of Ecology’s treatment window of July 15th.

A second treatment will occur after July 15 using Aquathol and Diquat. This treatment would focus on, 77 acres affected by Largeleaf Pondweed and Elodea. A 24-hour swimming precaution will be in place for treated areas, and an updated interactive map will be available for residents to check treatment locations.