Roesiger Invasive Aquatic Plant Control

The table below shows each of the plan elements and the actions being taken in 2023. All work will be managed by Snohomish County under the guidance of the Lake Roesiger Invasive Plant Advisory Committee (currently being formed). To stay up-to-date on the project, sign up to receive email updates.

Milfoil Plant Close-Up

Eurasian Watermilfoil 

5 year goal: Eradicate

Eurasian watermilfoil is currently in scattered locations in each of the three basins. The low densities are thanks to over two decades of diver surveys and hand-pulling. While these efforts have helped, they have not been consistent enough to eradicate this plant. 

2023 Actions: 

  • The County will work with contracted divers to conduct a thorough survey of the entire lake who will map and then hand-pull all located plants.
  • The Lake Roesiger community has established a volunteer dive team to assist with any additional plants found. 
  • You can help by reporting suspected milfoil plants here
Roesiger Draft Invasive Aquatic Plant Control Plan

Fragrant Waterlily Control

5 year goal: North and South Basins - Eradicate 

Middle Basin - 40 to 50% Reduction

Fragrant waterlily currently covers approximately 0.7 acres in the north basin, 0.6 in the south basin and 28.9 in the middle basin. 

2023 Actions

  • The County will obtain all necessary permits and then work with a contractor to begin herbicide treatments per the plan.  
  • Treatment areas will include all patches of fragrant waterlily in the north and south basins. Middle basin treatment areas will be finalized with the advisory committee according to the plan priorities. 
  • Final dates and locations will be communicated with the community before treatment occurs per the State's permit requirements. 
  • Landowners may choose to do additional control such as hand-pulling cutting etc. per WDFW's guidelines (note additional permits may be required for bottom barriers or other control methods). 
Boat draining on boat ramp to remove invasive species

Invasive Species Prevention

5 year goal: Prevent new introductions of invasive aquatic species

Lake Roesiger is a popular destination for boaters putting it at high risk for new invasive plant and animals to be introduced to the lake. Users leaving the lake can also spread Roesiger invasive species to other lakes. Outreach to boat users on how to Clean, Drain and Dry their boat is the best method to prevent the spread of invasive species. aquatic plants and animals into the lake

2023 Actions

  • Outreach campaign to Roesiger residents on how to prevent introductions (Clean, Drain and Dry your boats)
  • Coordination with advisory group and community on potential to have volunteers provide prevention education at boat launch on busy weekends.
  • Continued research into feasibility of boat cleaning station

Purple Loosestrife Patch and Flower

Shoreline Invasive Species 

5 year goal: Prevent further spread and reduce coverage

Invasive shoreline plants at Lake Roesiger include invasive knotweed, purple loosestrife and yellow flag iris. 

2023 Actions

  • Knotweed control - the Snohomish County Noxious Weed Control Board will continue to offer free treatment for properties with knotweed at Lake Roesiger. Contact for more information. 
  • Yellow flag iris & purple loosestrife - Landowners can take individual actions to reduce yellow flag iris and purple loosestrife
  • Additional educational workshops and outreach support on best control methods are planned for 2024.
Grass-leaved Arrowhead Patch and Flower

Slender Arrowhead 

5 year goal: prevent further spread and reduce coverage (initial target of 20% per year that would be scaled based on funding)

2023 Actions

  • The County will hire a contractor to begin Diver Assisted Suction Harvesting (DASH) to remove slender arrowhead. 
  • Exact treatment areas will be determined in conjunction with the advisory committee, but will include initial control by the boat launch to reduce risk of spreading to other area lakes. 
Milfoil Removal Boat

Project Success Monitoring 

5 year goal: Track the effectiveness of the project in meeting the project goals

2023 Actions

  • The County will conduct pre and post-treatment surveys (2024) of treatment areas to determine effectiveness of treatments in reducing invasive species and the re-establishment of native vegetation.  
Roesiger Draft Invasive Aquatic Plant Control Plan

Project Communications

5 year goal: Ensure community members are kept up-to-date on project actions and outcomes

2023 Actions

  • Create and maintain project website 
  • Send mailers:
    • Project kickoff mailer encouraging people to sign up for email updates and invite participation on committee
    • Permit-required notifications for herbicide treatments
  • Send email updates & NextDoor posts
    • Notification of upcoming plant control activities
    • Increase awareness of "Clean, Drain, Dry Boats" to prevent spread of invasive species 
    • Post-season summary of actions