Tahquamenon Falls asks visitors to topple rock towers

John Wisely | Detroit Free Press

Rock towers might be fun to build and cute to look at but they bug the bugs that live on the rocks — underwater.

They also bug the naturalists at Tahquamenon State Park, who are urging people to stop building them and topple them when they see them.

"Even though it seems like kind of small thing, when you're looking at 100 rock towers in the river, it does start to have an impact," said Theresa Neal, a park naturalist.

Neal said that insects like stoneflies, dragonflies and caddisflies use the rocks in the water to live and to hatch larvae. When people pull the rocks out of the water and stack them on top of one another, they reduce the habitat for the insects.

"An adult dragonfly eats mosquitoes, so we like dragonflies," Neal said. "Caddisflies, trout anglers really like them because trout really like them."

Rock towers, sometimes known as cairns, look like little mini Stonehenges. They are common along the Tahquamenon River in Michigan Upper Peninsula as well as along Great Lake shorelines, on Mackinac Island and anywhere else where water meets rock.

In many places they cause no harm, but in the Tahquamenon River, they have become a problem this year, Neal said. The park draws about 600,000 visitors each year and many of them wade into the river.

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"It's about 50/50," Neal said. "We have about 50 percent of our visitors who wade the water and the other 50 percent who think they're ruining the view," she said.

The park put a video on its Facebook page to illustrate the problem and remind people of the need of habitat for insects. The video generated dozens of comments, split pretty evenly between people who want fewer rock towers and others who think it's much ado about nothing.

Wading in the river is legal and anglers aren't the only ones who enjoy it.

Neal said it's not clear why the rock towers have been so common this year, but she said it could be related to a lower river flow. When the river is high and swift, fewer people wade into it. This year has been more low and slow, drawing more people to take the plunge.

"You always had a few of them but this year is the first time we really had a ton of them," Neal said. "Next season, we'll probably post signs."

Contact John Wisely: 313-222-2825 or jwisely@freepress.com. On Twitter @jwisely