Oak Creek Power Plant artificial reef

For the past two summers, Great Lakes WATER Institute scientist John Janssen has been keeping an eye out for yellow perch and lake trout at a Lake Michigan reef two miles east of Oak Creek.

The reef is one of many along the lake’s primarily rocky-bottomed western side, but it has one characteristic that distinguishes it from most others. It’s artificial.

We Energies built the reef two years ago as part of a project to expand its Oak Creek Power Plant. The U.S. Army Corps of Engineers required the reef as mitigation for habitat that could be lost when the utility constructed new lakebed structures, including a coal dock extension and water intake and discharge structures, said David Lee, We Energies’ water quality manager.

The intent is for the reef to become a spawning ground for perch and trout. Janssen is monitoring the reef as part of a five-year assessment study, required by the Army Corps and funded by We Energies, to determine if it is meeting that goal.

People have been building artificial reefs since at least the 1700s, when the Japanese placed bamboo structures underwater to attract fish for commercial harvest. Today, reefs are also built to provide habitat for aquatic animals and plants, to attract fish for angling, and as destinations for divers.

Artificial reefs have been built in both ocean and freshwater environments, with everything from logs and rocks to scuttled ships and New York City subway cars serving as building materials. Several reefs in Lake Erie, near Cleveland, Ohio, are made of rubble from the old Cleveland Browns stadium.

The Oak Creek reef, which is actually a cluster of six parallel reefs, is made of roughly 31,000 tons of quarried Wisconsin limestone, said Lee. The Edward E. Gillen Co., which specializes in marine construction, built the structures. We Energies did not disclose the project cost. Each reef measures about 600 feet long, 100 feet wide, and between 10 and 15 feet high. They are designed somewhat “like Twinkies,” said Janssen, with an inner core of three- to five-inch stones surrounded on the top and sides by a layer of 10- to 30-inch armor stones. The reef complex lies in about 50 feet of water.

Fisheries experts from several organizations, including the Army Corps, U.S. Fish and Wildlife Service, Great Lakes Fishery Commission, Wisconsin Department of Natural Resources, and WATER Institute, worked collaboratively on the reef design.

Developing the design required some educated guesswork-based largely on knowledge of natural habitats-because little precedent for building a spawning reef in Lake Michigan exists, said Janssen. The Great Lakes have relatively few artificial reefs, and the best studied of these-reefs constructed in Lake Erie’s central basin in the late 1980s and in Lake Michigan near Chicago in 1999-were built expressly to attract sport fish and promote angling.

Evidence of Perch Spawning

To evaluate the Oak Creek reef, Janssen and UW-Milwaukee graduate student Chris Houghton visit it several times each summer, looking for evidence of spawning and counting the number and types of fish they see during dives and catch by net. For comparison, they are also studying an adjacent sandy site, and the natural Green Can Reef to the north.

This year in early June, which is when perch spawn, they found perch eggs for the first time at the Oak Creek reef. They didn’t find trout eggs there last year, but hope to find some this year during trout spawning season in October or November.

They’ve spotted a variety of fish at the reef, including lake trout, alewife, longnose suckers, and smelt, but the most numerous fish have been yellow perch and round gobies. But, said Janssen, “right now it’s not at a density that will be a bonanza for fishing.”

The researchers are also inventorying the plants and small, invertebrate animals that attach to the reef rocks. The tiny animals provide food for young fish.

“That’s one of the primary things we want to compare with Green Can-do we get the same kinds of bugs, and do we get as many?” said Janssen. “There are rocks that have been out there two summers now and they don’t look anything like Green Can. They don’t have nearly as much algae on them, which is food for the invertebrates. So it’s still developing.”

But overall, said Janssen, the young reef so far looks promising. “In that fish are around there now and perch are showing up already, that’s a good sign. But if it’s going to be spectacular, it’s going to need a few years to develop,” he said. “This isn’t going to be instantaneous. It’s not just rocks-it’s the whole community that has to develop.”

Jennifer Yauck is a science writer at the Great Lakes WATER Institute. GLWI (glwi.uwm.edu) is the largest academic freshwater research facility on the Great Lakes.

A Tricky Issue

Artificial reefs are often thought of as a way to give new life to old ships, subway cars, and other materials while boosting fish populations and increasing opportunities for recreational fishing and diving. But artificial reefs can have downsides, too. Some scientists and environmentalists worry that artificial reef initiatives may be turning some coastal areas into underwater junkyards. There’s also debate over whether artificial reefs actually help produce more fish, or simply attract existing fish populations, thereby concentrating them and making them more susceptible to overfishing. Some ways people try to minimize the potential negatives of reef building are through careful planning, follow-up monitoring and assessment, and restrictions on fishing.

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