Lake Stevens has a history of invasive aquatic plants. In the late 2000’s, the lake was heavily impacted by Eurasian Milfoil. The City of Lake Stevens took the proactive step to begin addressing this problem in 2011. In the years since annual surveys have located and targeted remaining Eurasian Milfoil plants and the population has been significantly reduced. A second invasive aquatic plant was noted in the lake a few years ago. Curly Leaf Pondweed was observed for the first time in very low densities at a couple locations in the lake.

An ongoing program of survey and necessary noxious and nuisance treatment continues this year. During the week of July 21, 2025, weather permitting, there will be two herbicides used with a 24-hour swimming precaution.  Please be aware of signage only posted only in the treatment areas. 

Visit the Lake Stevens Noxious Aquatic Weed and Phosphorus Management Program page for more information, including an ArcOnline map for residents to review the treatment sites and determine if they are within one of them.