March 5, 2019
Spirit Lake – Invasive curlyleaf pondweed has become a common site in the spring on portions of the Iowa Great Lakes in recent years. The 2019 plan for managing this plant will be similar to 2018, but treat more acres.
A team of leaders from the county, local cities, lake associations, drinking water utilities, Iowa Lakeside Lab, and the Iowa Department of Natural Resources (DNR) have been working together over the past two years to manage this invasive aquatic plant that has caused water access and navigation issues on portions of the Iowa Great Lakes.
“Curlyleaf pondweed has been in our lakes since the middle of the last century, but conditions have allowed it to gain a foothold growing to form dense mats impacting recreation and access,” said Mike Hawkins, Iowa DNR fisheries biologist. “This plant is common throughout the Midwest, causing similar issues on hundreds of lakes.” Unlike native plants, curlyleaf pondweed germinates in the fall, grows under the ice and hits the surface by early May. It dies back naturally in late June.
Terry Wilts, with the East Okoboji Lakes Improvement Corporation, has helped spearhead the management effort over the past few years and explains there are no easy options to solve this problem.
“This plant impacts hundreds of acres. As a team, we realize we can’t treat all of it, but should prioritize our funds and efforts,“ Wilts said. “The 2019 plan builds on efforts from past years. We’ve taken what we’ve learned and are applying this knowledge to maximize our impact.”
The 2018 project treated 61 acres of curlyleaf with a combination of mechanical harvesting and the use of a aquatic herbicide. The 2019 plan includes a similar combination, but an increase in treatment area to 85 acres. The team was able to increase the number of acres while keeping the overall cost the same.
The 2018 project was considered successful. Boater access was improved and the project stayed on budget and on-time despite the late ice out. Twenty acres along the shoreline was treated with an aquatic herbicide and 41 acres (1 million pounds) was harvested using a mechanical plant harvester. The herbicide was used more than five miles from any drinking water intake even though water testing at the treatment area showed levels well below the drinking water standard right after treatment. The 2019 plan increases the herbicide treatment to 60 acres while still proposing mechanical harvesting of 25 acres.
The DNR and project partners want to emphasize the importance of not illegally applying herbicides.
“We can’t tolerate lakeshore residents illegally applying herbicides. Iowa law restricts their use and only the DNR has the authority to treat plants in the lake with a herbicide. Everyone living or vacationing in this area gets their drinking water from our lakes. Not following the law endangers that precious resource,” said Eric Stoll, with Milford Utilities, which supplies drinking water for thousands of customers in the region states.
Funding for the project will come from local contributions to the East Okoboji Lakes Improvement Corporation and the DNR’s Marine Fuel Tax Fund which is dedicated to improving boater access in Iowa.