A local environmental agency plans to dredge a Geneva Lake lagoon this fall to eradicate an invasive underwater plant threatening the lake.

Ted Peters, director of the Geneva Lake Environmental Agency, said the group last fall identified the invasive starry stonewort plant, an underwater macroalgae, in Trinke Lagoon on the lake’s south side.

It’s the first time the invasive plant has sprouted in Geneva Lake, Peters said. The plant is native to Asia and Europe and was likely brought to the continent by tankers plying the Atlantic Ocean.


Peters said starry stonewort is difficult to control because its bulbils are buried in the sediment and can’t be eradicated by chemical treatment. The lagoon must be dredged to stamp it out, Peters said.

Plans to dredge the lagoon this spring stalled after a company bid about $850,000, which Peters said was unacceptably high. The same company bid $174,000 to dredge the lagoon this fall.

Peters said the agency will open bidding May 13 for the fall dredging.

In the meantime, Peters said, the agency is asking people to avoid the lagoon until the plant is eradicated. They also are lobbying the state Department of Natural Resources to restrict access to the lagoon.

Peters said the agency does not have authority to do so because waters in the state are held in public trust. Additionally, Peters said, 35 to 40 boats are moored in the lagoon by local property owners, and closing it would cause a “significant inconvenience” to them.


Starry stonewort

Still, Peters wondered if the risks of spreading starry stonewort warrant the lagoon’s temporary closure.

If the plant is spread to the entire lake, Peters said, it likely would be difficult to eliminate and would alter the biological community, changing the environment such that fish and native critters could not survive.

“It will out-compete the native species and send a ripple through the whole food chain,” he said.

Dredging the lagoon will require screening off its channel to the lake. A large vacuum-like machine will suck about 2 feet of sediment from the bottom of the lagoon, Peters said.

The dredged material will be pumped to large watering bags, which will trap the sediment and plants’ bulbils. Access to the lagoon will be restricted for about two weeks after Labor Day during dredging, Peters said.

Two chemical treatments this summer will shut down the lagoon for 10 days. That will be done to exterminate the plant on the surface, but it will not kill the bulbils.


Star-shaped bulbils are produced at the nodes of the starry stonewort. The plant was recently discovered in Trinke Lagoon along Geneva Lake’s south shore.

Sixteen lakes in Wisconsin are verified to have starry stonewort, according to the DNR, including two in Racine and Waukesha counties. Six lakes in Door County are verified to have it. It first appeared in Wisconsin in 2014.

Peters said the plant is spread when bits of it are carried from an area by boat. Bulbils also can be transported by water, mud or boat anchors.

Geneva Lake has seen cases of zebra mussels, Eurasian watermilfoil and curly-leaf pondweed, all of which are invasive aquatic plants, Peters said. By comparison, starry stonewort is much more aggressive, he said.

“What we really want to do is make the public aware of this plant ... and to maybe make a personal sacrifice of not fishing in this area until next year because the risk of doing so could affect the whole lake,” Peters said.


Ted Peters, director of the Geneva Lake Environmental Agency, looks out onto Trinke Lagoon, where the invasive species starry stonewort was discovered in fall 2018. The agency plans to dredge the lagoon this fall in an effort to eradicate the threat the microalgae poses to the lake.

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