Invasive plant that can inhibit navigation found in 5 northwest Iowa lakes

The Iowa Department of Natural Resources has found an invasive plant called Eurasian watermilfoil in five northwest Iowa lakes.

Eurasian watermilfoil can grow up to 20 feet tall, spreads rapidly and crowds out native plants that grow underwater. Mike Hawkins of the Iowa DNR says the plant was first found in Lost Island Lake on August 1.

“Eurasian watermilfoil is very aggressive,” Hawkins says. “It can create some large mats of floating plants. It’s a plant that’s rooted in the bottom but can make it to the surface and can cause some navigation issues.”

Teams have already treated the four areas of Lost Island Lake where the invasive plant was spotted.

“Using herbicides in large lake systems is very difficult because of the amount of herbicide that’s necessary and the cost,” Hawkins says, “and application that has to be done is very, very precise.”

The DNR now confirms the plant is growing in four of the seven Iowa Great Lakes. Hawkins says the natural lakes are in good shape to resist the spread of this plant.

“Think about your yard, for example, if you were to just dig up all of that big section of front yard and just let it go, the first thing that would colonize to it would be the weeds, the undesirable things — invaders,” he says. “The same thing can happen in a lake, but if that lake is very healthy and has a diverse aquatic plant community of native plants, it’s much harder for a plant like Eurasian watermilfoil to take a strong hold.”

The initial treatment plan for both Lower and Upper Gar, East Okoboji and Minnewashta Lakes will focus on the areas around boat ramps, to make sure the plant is killed in an area where it could be taken to another location.

“If somebody leaving that area, for example, had the plant attached to their boat or trailer, they could trailer it down the road and introduce it into a new water body,” Hawkins says. “In that specific area we’re going to do a very quick treatment in the coming days and then we’re going to develop a larger strategy, both short term and long term, for the lakes.”

Washing boats and trailers after leaving a lake and letting them dry for five days helps keep invasive species from spreading. Hawkins says frequent surveys have been done on other nearby lakes, but so far the plant hasn’t been found elsewhere.

(Reporting by Adam Gellert, KICD, Spencer)