Flint Lake on Valparaiso’s north side is in trouble. Invasive aquatic weeds, especially Eurasian milfoil, have become so overgrown that they’re even interfering with fish population surveys. During a recent Department of Natural Resources (DNR) survey, biologists had to stop two or three times just to clean the weeds off their boat’s propellers.

Herbicide Treatments: A Short-Term Fix with Long-Term Consequences

While treatments for Eurasian milfoil might seem like a good solution, they often come with serious environmental trade-offs. Herbicides do not actually remove the plants—they simply kill them where they grow. This leaves large amounts of decaying plant matter in the water, which can significantly reduce oxygen levels. As the plants rot, they consume oxygen that fish and other aquatic life depend on, potentially creating dead zones that are uninhabitable.

To make matters worse, the milfoil in Flint Lake is becoming more resistant to the most commonly used chemical treatments. And if the herbicide isn’t specific to milfoil, it can endanger beneficial native plants as well.

Native Plants: Critical for Young Fish and Water Quality

These native aquatic plants are more than just vegetation—they’re lifelines for young fish. “Anytime you damage these plants, you’re killing hundreds of thousands of babies,” DNR specialist said. Smaller fish use these plants to hide from predators and as feeding grounds. Destroying them reduces fish survival rates and upsets the balance of the ecosystem.

Mechanical Removal Isn’t a Silver Bullet Either

Even mechanical methods have their risks. Fragmenting Eurasian milfoil—chopping it up—can actually help it spread. Each small piece of the plant has the potential to take root and grow elsewhere in the lake.

A Call for Smarter Management

The situation at Flint Lake underscores the urgent need for responsible and effective aquatic plant management strategies. It’s not enough to kill the plants—we must remove them in a way that protects fish habitats, promotes water quality, and prevents further spread.

Water chestnut (Trapa natans) is native to Asia, Europe and Africa. It was introduced in 1897 by a gardener as an ornamental plant in Fresh Pond in Cambridge, Massachusetts. Since then, it has spread to rivers and lakes throughout the commonwealth. Eradication efforts of water chestnuts in the Mystic River have been ongoing.

MyRWA is happy to report that in 2014 it had its most successful year yet! More than 940 volunteers hand-pulled 6,603 baskets of water chestnuts and the aquatic plant harvester removed 1,000 tons of water chestnuts this year.

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The weed’s invasion is driving heated debates about how to control it — from using mechanical removal to administering herbicides that raise concerns about drinking water safety.

An aquatic weed harvester has logged 300 hours this spring, chopping and pulling out about 450,000 pounds of weeds from East Okoboji Lake.  The plants are drying in a couple of remote spots, with the hopes that farmers might be able to use them for fertilizer.

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Curly-leaf pondweed is an invasive plant found throughout much of Minnesota. The plant grows slowly throughout the winter under the ice, but once the ice has left the lake the plants start to grow very rapidly. Curly-leaf pondweed gets a jump start on native aquatic plants, leading to dense mats on the surface by May or June. Sometime around mid-July, curly-leaf pondweed dies off and decomposes in the lake.

In the past, many lake managers thought that early treatment of curly-leaf pondweed might lead to better water quality and improved native plant populations. However, recent research has proven that large scale treatments in lakes with high nutrients levels did not produce water quality benefits or increase native plant populations.

Herbicide control is restricted to 15% of the littoral area of the lake, but mechanical harvesting allows for up to 50% of the littoral area of the lake to be harvested. A combination of both methods may be used as well. A limit on what areas to be treated or harvested insures that native plants, which provide water quality and fish and wildlife habitat benefits, will be protected.

Curly leaf pondweed grows under the ice during the winter, but in the summer months it dies off after it reproduces. As it dies and decays, the plant releases nitrogen which causes algae blooms. These algae blooms cause water restrictions, illness, and fish kills.

Over 250 tons of curly leaf pondweed were removed from Lake Wausau, in Wisconsin, over the last four years and taken to the city dumpsite where people can pick up to be used as fertilizer in their gardens.

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The plant is injurious with its four-headed needle-sharp seeds typically making it to shore and cutting the feet of those who walk on them. But the removal and control of the plant is not easy. The sticky water chestnut seeds are carried by ducks, geese and other animals from waterway to waterway, making elimination of the weed difficult.

Dickson and others who worked with him have vigorously worked for years to get Bare Hill Pond’s water chestnut weed population down, hosting three volunteer weed pulls a year at one time. He also used the town’s mechanical weed harvester. “We picked up 80 tons of weeds with the harvester one year. The next year, 20 tons, and the next just five, until we didn’t need the harvester anymore.”

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Curly-leaf pondweed is an invasive plant found throughout much of Minnesota. The plant grows slowly throughout the winter under the ice, but once the ice has left the lake the plants start to grow very rapidly. Curly-leaf pondweed gets a jump start on native aquatic plants, leading to dense mats on the surface by May or June. Sometime around mid-July, curly-leaf pondweed dies off and decomposes in the lake.

In the past, many lake managers thought that early treatment of curly-leaf pondweed might lead to better water quality and improved native plant populations. However, recent research has proven that large-scale treatments in lakes with high nutrients levels did not produce water quality benefits or increase native plant populations.

Herbicide control is restricted to 15% of the littoral area of the lake, but mechanical harvesting allows for up to 50% of the littoral area of the lake to be harvested. A combination of both methods may be used as well. A limit on what areas to be treated or harvested ensures that native plants, which provide water quality and fish and wildlife habitat benefits, will be protected.

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In 1982 the association purchased their first weed harvester and trailer, which was replaced in 1994 by a larger, but used 1987 Aquarius Systems 620 harvester, that is still in use today.  The association does not receive state funds to run the harvester; it is financed by membership, business, and other local group donations along with fund raisers.  The work required to run the machine is immense and there are a lot of donated hours by board members and volunteers to keep the equipment running.

Three months out of the year the harvester runs five days a week about 8 hours a day (weather permitting) to maintain the 4,500 acre lake.  Not all of the lake gets cut either, there are designated no cut areas established by the DNR and certain native plants aren’t cut like lily pads, wild rice, and bulrush.  Since the harvester has been in use not only has the amount of weeds decreased, but water clarity has significantly increased as well.

A big reason for this is because there are fewer weeds dying in the lake and decomposing to the bottom.  If the vegetation is left to rot, the nutrients in it that have been absorbed from the water are released back to the water column and become nutrients for the next weed growth or algae bloom. But something far worse occurs; as the vegetation decays, it uses up the oxygen at the bottom which affects fish as well as native plants.  The weeds contain a huge amount of phosphorous which is being removed along with the weeds, the more phosphorous in a lake, the more algae growth, therefore the lower water clarity.

Some people in the area don’t believe in the weed harvester and feel that cutting the weeds leads to more growth, but Steve Olson, LMA board member disagrees.  “If that were the case, then they would have never needed to harvest here in the first place.”  Other people have suggested controlling the weeds with chemicals instead of the harvester, but the cost is very prohibitive with a price tag of half a million dollars compared to the $25,000 a year it takes to run and maintain the weed harvester.

With the aid of the Aquarius Systems weed harvester and 18 years of sufficient lake improvements, Save Minnewawa Association officially changed their name in 1995 to Lake Minnewawa Association (LMA).

Wednesday, August 1, 2007