Invasive aquatic plants spread across northeast Wisconsin waterways

NORTHEAST WIS. – An aquatic plant once used for greenery in aquariums has invaded inland lakes in northeast Wisconsin, tangling up boat propellers and clogging the flow of oxygen to native species.

Eurasian water milfoil grows quickly and can change a lake’s ecosystem, said Steve Heimerman, board member of the Oconto County Lakes and Waterways Association. The group is working to halt the spread of invasive species that could affect the value of lake property.

“Who wants to live on a swamp?” he asked. “It totally covers the area with a thick bed of weeds you can’t boat through, you can’t fish through.”

Unaddressed, the Eurasian water milfoil problem is likely to worsen, he said. “It’s going to catch up to us.”

The best time to address a potential invasive species issue is before it gets into an inland lake, experts said. “Once you have them, it’s a management issue. It’s almost impossible to eradicate an invasive species once it gets in a lake,” said Chuck Druckrey, Marinette County water resource specialist. Signage on the Bay of Green Bay alerts boaters to clean their boat wells so they don’t inadvertently transport an invasive plant from the bay to an inland lake.

Eurasian water milfoil is the invasive species with the highest “cost-pain,” Heimerman said, but they’re not the only problem.

“Anything I mention to you is in the Bay, and many came into the lakes from the Bay,” he said. “Every lake is different.”

Volunteers and summer workers have been stationed strategically at boat launches to instruct boaters how to clean and dry their boats before transporting them. In the past, Marinette County received funding to monitor European frog-bit by educating boaters and anglers on how to prevent the invasive species from spreading, Druckrey said. This year, it doesn’t have summer interns helping with the program.

So far, European frog-bit hasn’t infiltrated most Marinette County lakes yet, Druckrey said, but it was found in Oconto County in 2021, according to the Wisconsin Department of Natural Resources. Its leaves resemble small lily pads and it has small white flowers when in bloom, the DNR said. “It likes deep water marsh areas that ducks would be using,” Druckrey said.

Marinette County also is on the lookout for curly-leaf pond weed, an invasive species that’s been an issue in southern Wisconsin, Druckrey said. The aquatic plant has narrow olive-green and reddish-brown leaves about a half-inch wide and up to three inches long. So far, it hasn’t been spotted in Marinette County inland lakes, he said, but Eurasian water milfoil is a common issue.

When invasive plants become too thick in inland lakes, fishing becomes a challenge, said Oconto County Conservationist Ken Dolata. While Oconto County once had five bass tournaments on the calendar, most are no longer offered, he said. The 7th Annual Ed Tank Memorial Bass Tournament is scheduled for June 21 from 6 a.m. to noon at 9291 Lee Lake Road in Oconto County.

Dolata said he is pursuing a water resource specialist position to work with lakes and streams in the county. “It gets to be a hard problem for the county. If you let the lake go and water quality decreases, it’s proven property prices go down,” Dolata said.

Besides the Eurasian water milfoil, some Oconto County lakes also have flowering rush and European frog bit, Dolata said. The county helps local lake associations treat invasive species, but most haven’t been wiped out, Dolata said.

Oconto County offers grants for preserving the waterways of up to 10% of the cost of treatment with a cap of $7,000.

“Managing the invasives is a year-round job,” Heimerman said. It involves studies, pre- and post-treatment surveys, lining up vendors to apply treatments and writing grants for funding, he said. “It’s a big job. It means a lot of time for people who may not have any experience with it,” Heimerman said.

For Eurasian water milfoil, the most effective treatment is applying chemicals directly into the lake. “Once [water milfoil] gets to a certain state of taking over the lake, there is no other process that works,” he said.

The treatments aim to keep the Eurasian water milfoil from spreading.

About 29 of the over 65 lakes in Oconto County have an infestation of Eurasian watermilfoil, Heimerman said. Seventeen are involved actively in treating it, mostly with chemical treatments, he said.

Depending on the size of the lake, chemical treatments can cost tens of thousands of dollars.

Another method involves hand harvesting, or Diver Assisted Suction Harvesting, where divers find the weed by its roots and suck it out with a giant suction hose, he said.

Addressing the problem starts with identifying the feathery leaves and slender stems that grow underwater with roots attached to the lake bottom. Its blooms are pink.

Understanding how it sneaks onto boats, often unbeknownst to boaters, is important to controlling it.

Once the invasive species has found a home in an inland lake, it doesn’t give it up easily.

In Marinette County, Druckrey said he has harvested Eurasian water milfoil from the lakebed using the county’s Diver Assisted Suction Harvester. The process involves guiding the milfoil into the harvester’s suction hose to be transported to the surface, he said.

Beecher Lake, Newton Lake and Thunder Lake are routinely treated to control the water milfoil, he said. They all have public boat ramps.

On Thunder Lake, Marinette County has installed a barrier of herbicide to treat areas where the milfoil is thick. “The barrier prevents the herbicide from dispersing throughout the lake and improves treatment effectiveness,” he said. Private contractors also have applied aquatic herbicide in Thunder Lake to control the milfoil, he said.

Druckrey said his department is working with a Thunder Lake association a new Aquatic Invasive Species Management Plan that could help to secure funding, such as a state grant, and to do herbicide treatments. “We spend a lot of time helping them with the management and with grant applications,” he said.

The Wisconsin Department of Natural Resources requires lake associations applying for funding have a comprehensive plan and an aquatic management plan targeted at plant life or natural life.

Dolata said Oconto County studies six lakes per year and produces shoreline surveys and 10-year water resource plans.

With Eurasian water milfoil brought into local lakes from various boaters who have boated on other lakes, many local lake residents believe the government should share in the treatment costs. “Why should the property owners have to pay for everybody else’s use of the lake?” Heimerman said.

Some lakes have in the neighborhood of 100 residents, and most live elsewhere during the winter months, Dolata said. Even if they secure a grant from the Department of Natural Resources, it won’t be for the full amount of the treatment, leaving residents to foot a sizable portion of the cost or raise the funds.