Sunday Lake Invasive Plant Control

 County assistance for Sunday Lake Fragrant Water Lily Control

The Sunday Lake Organization requested assistance from Snohomish County for invasive lily control. The County was able to secure funding and offered the organization assistance for efforts in 2022 and 2023. The assistance includes paying for and managing the invasive plant treatments. 

2022-2023 Control Efforts

The County contracted with AquaTechnex, a licensed aquatic herbicide applicator, to perform treatments for fragrant waterlily control; 15.5 acres were treated in 2022 and 7.5 acres were treated in 2023.

These treatments have been highly successful and provided relief in many areas, but continued work by residents is needed. Work must be done to address any remaining lilies until they are eradicated, or the lake will be at a high risk of re-infestation. Needed control efforts may include repeated cutting or other manual control methods. Additional herbicide treatments may also be needed should any larger patches remain. 

Unfortunately, the County does not have funding for treatments in 2024 but can continue to provide technical and permitting assistance. County lakes staff will also be conducting a plant survey in the spring of 2024 to assess the treatment effectiveness.

The Issue

Sunday Lake is home to an abundance of native plants. These beneficial plants are vital to keeping lakes healthy. They provide important food and habitat for aquatic life including fish, turtles, frogs waterfowl and other aquatic life. They also are important for us as they help to clean the lake by filtering pollution and prevent shoreline erosion. 

Unfortunately, Sunday Lake is also home to a few non-native invasive plants including fragrant water lily and yellow flag iris. These plants can crowd out the beneficial native plants, harm lake ecology, and interfere with swimming, fishing and boating. So while it is important to keep native plants in the lake, it can be desirable to manage invasive plants to reduce their impacts. Learn more about how the different types of aquatic plants and how to identify them. 

Invasive Lily Control Efforts at Sunday Lake

Over the years, residents have worked to control invasive fragrant waterlilies in front of their properties by hand-cutting, pulling out the roots and using an aquatic mower. However, the  infestation continued to grow covering the majority of the lake. In 2018, a group of residents formed the Sunday Lake Organization to advocate for the long-term health of the lake and the initial goal of addressing the lilies.


With funding from local residents, the group obtained a state permit and contracted with a licensed aquatic herbicide applicator to treat the invasive lilies. Treatments have occurred each summer in 2019-2021. In 2022, The County took over the state permit and treated over 15 acres of lilies.

Multiple years of treatment are needed as only a portion of the lilies can be treated each year. These treatments have been highly successful and provided relief in many areas, yet continued work is needed to address the remaining problems. 

Fragrant waterlily was introduced as an ornamental plant. It takes over shallow areas, limits habitat and boating, and causes the lake to fill in faster.

Fragrant Waterlily Patch and Flower