Iowa DNR to eliminate invasive plant in Iowa Great Lakes


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Grace Smith | September 20, 2022

The Iowa Department of Natural Resources plans to start treating East Okoboji, Upper Gar, Lake Minnewashta, and Lower Gar this week with Sonar A.S., an aquatic herbicide, to eliminate Eurasian watermilfoil, an invasive plant. Eurasian watermilfoil was found in these lakes in early August. The DNR will test the water every two weeks through next Spring, per a release published on Sept. 13. 

The DNR wants to remove the Eurasian watermilfoil because it is an aggressive and invasive plant known to take over the space where native plants would normally be. By eliminating the Eurasian watermilfoil, the DNR will use Sonar A.S., which prevents the plant from producing a pigment needed for photosynthesis. This process would eventually starve the plant over a few weeks. The DNR said the herbicide has no restrictions for swimming, fishing, irrigation, or drinking water at the planned dose. 

An East Okoboji Lakes Improvement Corporation representative told Radio Iowa the plant has been found in fairly abundant amounts in certain spots. To keep the species from spreading, the representative said washing boats and trailers after leaving a lake can help. 

A group of people from Iowa Great Lakes organizations is helping the DNR formulate a plan, and local groups are partnering to donate $335,000 toward the elimination of the invasive plant. 

“Keeping the plant out of the lakes over the past 30 years has allowed time for better tools to be developed for managing this plant,” said Mike Hawkins, district fisheries biologist with the Iowa DNR. “I’m confident we can work together locally to manage it long-term. In the meantime, we plan to take our best shot at eliminating it.”