The left image shows East Troy Lake before it was drawn down in late 2015. The right image shows the lake today, with weeds poking through the water's surface from where they grew during the drawdown.

'Don't end up like we did:' East Troy residents caution Janesville on dam removal

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Jake Magee
Sunday, May 14, 2017

EAST TROY—The Rostkowskis didn't expect the drastic changes they saw when the East Troy Lake was drawn down in late 2015.

They knew weeds would grow where the water once was, but they didn't foresee the size or density of the vegetation. Some reach 10 feet tall, they said.

“You wouldn't have been able to see me out there when I was mowing,” said Steve Rostkowski, East Troy Lake Association president and Walworth County Lakes Association member. “I would literally disappear.”

“We were all surprised how high it could get,” said Jan Rostkowski, Steve's wife.

The water has since been restored, but weeds still poke from the surface of the water, giving the lake more of a marshy appearance.

Janesville could see a similar vegetative explosion when the Monterey Dam is removed next year, but officials say they won't let that happen. The city has plans to restore the area and prevent weeds from overtaking the affected shoreline, officials said.


The 29-acre East Troy Lake is created by a dam that holds back Honey Creek. The state Department of Natural Resources classifies it as a pond, but the Rostkowskis, who live on the lake's north shore, said the water body recently was reclassified as a lake.

In late 2015, officials opened the dam on the lake's west side to repair the dam and conduct a phosphorus study. The downstream water treatment plant wanted to log phosphorus levels without the lake as a variable, the Rostkowskis said.

Officials decided to repair rather than remove the dam, which exists only to create the lake, because several residents who lived along the lake wanted it to remain, among other reasons, the Rostkowskis said.

The lake had been drawn down before, but not for more than a couple months.

“We were a little surprised that it was going to be one year, but we were happy that they were willing to repair the dam, too,” Jan said.

The lake receded, leaving a thin stream of Honey Creek. It didn't take long for weeds to grow.

Cattails and wild parsnip took root. By the summer, some weeds were taller than Steve.

Steve mowed the weeds near his property line. He also mowed a path through the foliage to the creek so his row boat would be able to reach the channel after the water was restored.

Throughout the one-year draw down, residents questioned the wild weed growth.

“A lot of people commented from the community, 'What are they going to do about your lake?' It was unsightly,” Jan said.

Officials considered combating the weeds with controlled burns and by periodically restoring the water to drown the weeds, but those suggestions were denied, the Rostkowskis said.

“We just had to endure,” Jan said.

The water was restored in November 2016. Six months later, the tall weeds stand in the water. The Rostkowskis don't know when, if ever, the lake will return to its former quality.

“We've been watching the (Monterey) dam articles, and we're just thinking, 'Don't end up like we did,'” Jan said.


Local officials said Janesville's situation is different.

For one, the village of East Troy drew down its lake knowing it would restore the water and therefore didn't implement plans to curb weed growth. Janesville, knowing the Monterey Dam will be gone forever, has plans to make sure the area doesn't become weedy, said stormwater engineer Tim Whittaker and Public Works Director Paul Woodard.

After the Monterey lagoon and Rock River upstream of the Monterey Dam are drawn down for dam removal, the city will wait for the new shoreline to dry out before grading it to the desired shape.

A cover crop and native vegetation such as grasses, flowering plants, clover and milkweed will be planted on the river's north side just upstream of the dam.

“We're going to plant what we want to see there,” Whittaker said.

Establishing a new seedbed in the sediment will out-compete whatever seedbed already exists, but part of the city's management plan is to control any weeds that do pop up, Whittaker said.

The city will do the same type of work behind homes on Main Street on the river's east shore, he said.

Further downstream where the river turns west, the south shoreline doesn't abut residences or recreation areas. In that area, the city will take a passive approach and let the shore revert to a more natural state. Officials will install a cover crop, but the city will wait and see what happens with the existing seedbed, Whittaker said.

The idea for a passive approach to some of the shoreline came from other communities that have removed dams. Municipalities in Milwaukee County have told Janesville officials they've had success in letting whatever plants are in the sediment grow, Whittaker said.

The village of East Troy had the luxury of seeing what could happen if its dam were removed, but Janesville doesn't. Officials have said it's impossible to draw down the Rock River without removing the Monterey Dam because the dam's gates are too small.

Still, the city will respond if weeds grow wild or invasive species take root, officials said.

“This is not going to be like a one-time planting, we're done,” Woodard said. “It's going to take a few years to go back and forth.”

After the shorelines are restored, there are plans to dredge the existing Monterey lagoon to make it a stormwater pond with a peninsula in the middle. The pond will catch rain runoff and pollution before it reaches the river, Whittaker said.

To anyone concerned about weed growth similar to that seen near East Troy Lake, officials pointed to how Janesville manages other natural areas, such as the greenbelt and other stormwater ponds.

“We've been pretty responsive to resident concerns,” he said.

In early June, the city will put together a work team of residents, downtown stakeholders, a city council member and city officials to work with shoreline restoration consultant Inter-Fluve to finalize conceptual shoreline plans, Woodard said.

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