The Mystery of the “Fairy Rings” on Howe Lake

What’s behind these curious fairy rings on Howe Lake? Photo: S. Knight

by Sydney Widell — Howe Lake is hard to get to.

It lies at the end of a narrow, rutted-out dirt road, ten miles from the nearest town. And it’s not just physical distance that makes it so challenging to visit.

Howe Lake sits in the Huron Mountain Club, a gated retreat and old growth forest reserve located on Lake Superior, roughly 35 miles northwest of Marquette, in Michigan’s Upper Peninsula.

If you wanted to see the lake, you’d have to be one of the club’s 50 standing or associate members. Or Susan Knight, botanist and Trout Lake Station director, who was allowed to visit the area last week to research a mysterious plant formation she’d heard about there.

Susan’s adventure began last year, when her former advisor at UW-Madison sent her a photo of Howe Lake, and a peculiar circle of plants growing on it. 

“It was a very poor photo, actually, of what looked like rings of pond lilies on this lake, like donut rings with nothing in the middle,” Susan remembers. “My advisor asked what I thought would have caused this, and I didn’t know.”

So Susan decided to check it out.

Susan (middle, left) with fellow botanists Carol Warden, Barb Gajewski and Michelle Nault (left to right) at Howe Lake. Photo: S. Knight

“It was just so curious,” Susan said. “I look at aquatic plants all the time and I’d never seen anything like this. I just thought, ‘oh my gosh, we have got to go figure out what is going on!’”

It turned out that the Huron Mountain Club allows a small number of outside researchers onto the property every year through a science foundation program. Susan submitted a proposal and was awarded a small grant.

Last week, she finally had the opportunity to make the three and a half hour trip up from the Northern Highlands to the Huron Mountain Club for three days of research. With her was Carol Warden, a Trout Lake Station invasive species specialist,  Michelle Nault, a WDNR aquatic biologist and Barb Gajewski, an environmental consultant based in the Upper Peninsula.

The property truly is gated. When they arrived, they were admitted by a guard and instructed to drive down a long, unmarked dirt road that led to the place they would be staying — a turn of the century building called The Stonehouse.

“It was very, very remote, but also spectacular,” Susan said. “It was really quiet.”

Howe Lake was even harder to find.

“It was pretty good that we had four-wheel drive,” she said. “It was a bit of an effort to get to the right lake, but we finally did.”

But as remote as the Howe Lake site felt, they arrived to find a boat house and five wooden rowboats waiting for them on the shore. The Huron Mountain Club does not allow outside boats to run on property, so Susan and the other researchers used these to do their sampling.

Watershield fans out in a ring like a corona around the sun. Susan and her co-investigators left unsure exactly why the plants grew like this, but they are excited to keep studying the remarkable formations. Photo: S. Knight

The fairy rings were roughly 30 meters across, larger than they had looked in the pictures, and made up entirely of water shield, an aquatic plant found abundantly across northern Wisconsin and the U.P.

“When we saw the real rings, they were really distinct and green and it was like a sunburst,” Susan said. “There were a few plants spreading out from the outside edge, like the sun’s corona, which was kind of surprising.”

Also surprising was that the watershield was one of the only things growing in the water, which Susan said was unusual.

One factor that may have made the lake such an inhospitable place for plant growth was the watery, soup-like sediment covering its bottom. Although the lake itself was only a meter deep at its center, Susan estimated that the sediment went down for several more feet — making it hard for plants to root.

Another is that watershield, with its spade-shaped green leaves that float like lily pads on the surface of the water, shades out other species growing in the water column, Susan said.  

Originally, Susan had wondered if a cold spring in the center of the lake had caused the watershield to grow in this peculiar formation around it.

“My original idea was that at the center of the ring there was a spring that was coming up forcefully with very cold water,” Susan said. “The reason there was a ring was because it was too cold for the plants to grow.”

To test her idea, she and the other researchers measured the temperature inside and outside of the ring, and checked for dissolved oxygen, minerals like calcium and a few other indicators.

But, so far, the team hasn’t been able to confirm their first theory.

“Some of those analyses aren’t done yet, but so far nothing is really popping out at us,” Susan said.

Susan and her team left the Huron Mountains with just as many questions as they’d had when they got there. If a spring wasn’t what was causing these fairy rings to form, then what was?

Susan’s new theory is that as the watershield grew, it used up the nutrients around it. The only direction it could spread was outward, leaving a hole in the center where the old growth died off.

“If we get a chance to go back, that’s what we want to test,” Susan said. “What we’re exploring now is trying to get some Google Earth imagery of these lakes from other years to see if we can see these rings from years ago.”

For now though, Google Earth is as close as she’s going to get in her quest to solve this murky mystery.