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Iowa DNR will treat Iowa Great Lakes for invasive Eurasian watermilfoil

  • 8/9/2022 2:18:00 PM
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SPIRIT LAKE - The Iowa Department of Natural Resources (DNR) confirmed Eurasian watermilfoil is growing at multiple locations in East Okoboji Lake, Upper Gar Lake, Lake Minnewashta, and Lower Gar Lake in Dickinson County.

The Iowa DNR Aquatic Plant Management team monitors 153 sites at the Iowa Great Lakes each year. Each site is visited twice each year to detect invasive plants in early stages of growth and allow the DNR to quickly develop management plans to control the plants. 

Surveys conducted in Spirit Lake, Center Lake, and West Okoboji Lake did not detect Eurasian watermilfoil.

Additional surveys were conducted after Eurasian watermilfoil was discovered to determine the spread of the plant. 

“We are aggressively developing a management plan to immediately treat areas of the lakes where the plant has been detected with an aquatic herbicide approved for use on lakes and drinking water sources,” said Mike Hawkins, Fisheries Biologist for the Iowa DNR. “These aquatic herbicides have very few label restrictions. Contact with the water after treatment is safe for fishing or other recreational activities.”

Eurasian watermilfoil, an invasive rooted aquatic plant native to parts of Europe and Asia, can spread quickly and outcompete beneficial native plants. It reproduces by fragmentation, which means small pieces of it grow into new plants and form thick beds.

The DNR has been working closely with the community to treat curly-leaf pondweed each year in East Okoboji Lake, Lake Minnewashta, and Lower Gar Lake. Eurasian watermilfoil represents another immediate challenge for these lakes. The timing and methods for treatment of curly-leaf pondweed differs from Eurasian watermilfoil. 

Iowa’s Aquatic Invasive Species Program has been a national leader in control efforts to stop Eurasian watermilfoil for the past 30 years. “Iowa DNR has successfully eradicated the plant in many lakes throughout the state.  However, the size and complexity of the Iowa Great Lakes will present real challenges for management,” explains Hawkins. “Lakes with healthy, diverse native aquatic plant communities may be less susceptible to an infestation that takes over the native plant community.” 

 “Boaters and anglers can unintentionally spread Eurasian watermilfiol and other aquatic invasive species if they do not take the proper precautions - clean, drain, dry - after each time out on the water,” said Kim Bogenschutz, the DNR’s aquatic invasive species program coordinator.

  • CLEAN any plants, animals or mud from the boat and equipment before you leave a water body.
  • DRAIN water from all equipment (motor, live well, bilge, transom well, bait bucket) before you leave a water body.
  • DRY anything that comes into contact with water (boats, trailers, equipment, boots, clothing, dogs). Before you move to another waterbody either: Spray your boat and trailer with hot, high-pressure water; or Dry your boat and equipment for at least 5 days.
  • Never release plants, fish or animals into a water body unless they came out of that water body and empty unwanted bait in the trash.

It is illegal to possess or transport prohibited aquatic invasive species, such as Eurasian watermilfoil, in Iowa. Boaters must also drain all water from boats and equipment before leaving a water access and must keep drain plugs removed or opened during transport.

Find more information about aquatic invasive species and a list of infested waters in the 2022 Iowa Fishing Regulations booklet or on the DNR’s website at