We Energies Builds Barrier Reef at Oak Creek Power Plant Project

By Sean Ryan

As part of its Oak Creek power plant project, We Energies is building a barrier reef that, it hopes, will serve as a buffet and love nest for Lake Michigan’s yellow perch.

But most simply, it’ll be a 31,500-ton distraction that will attract fish away from the power plant’s water intake and discharge pipes, said John Janssen, senior scientist at the University of Wisconsin-Milwaukee Great Lakes Water Institute.

This reef will not be a pile of rocks – engineers and scientists put a lot of thought into designing this thing. Scientists at the UWM Water Institute worked with the state Department of Natural Resources and U.S. Fish and Wildlife Service. They based its design on evaluations of a man-made reef off the coast of Chicago and studied the natural Green Can Reef off Milwaukee’s shoreline.

“There is a distinct impression that a lot of the artificial reefs are just an excuse to dump stuff out in the lake,” Janssen said. “Some reefs have worked and some haven’t, and we don’t really know why.”

It’s not easy building a home for yellow perch in Lake Michigan because the creatures were around before glaciers carved out the Great Lakes. They evolved to live in the slow-moving parts of rivers and among the leafy underwater plants in inland lakes, Janssen said. Perch weren’t built for the open water, so they tend to congregate around reefs, where it’s easier to find a decent meal of gnat-like midges and tiny, shrimp-like amphipods. Lake Michigan is a rarity among the five Great Lakes because its populations of perch actually live in the deep waters away from shallower and warmer bays, Janssen said.

50-feet deep

We Energies’ reef will be two miles due east of the Oak Creek power plant in water that’s about 50 feet deep. It’ll have six separate reefs, each 540 feet long and 140 feet wide and standing 10 feet high, said Dave Lee manager of water quality at We Energies. The six reefs will be arranged parallel to each other so fish can swim between them, but also a little staggered to create a wider footprint so they’re easier for perch to locate, Janssen said.

“I’d say it was an educated guess as to what would be the best design,” he said.

Crews from Edward E. Gillen Co. will build the reefs by first dumping 20,000 tons of five-inch chunks of limestone into the lake to create the basic footprint of the six separate reefs. Then they’ll bring in 11,500 tons of larger, 20- or 30-inch stones called riprap to create the outer layer of each reef.

“They’ll be self-unloading barges, so the rock will be conveyed over the side -essentially just poured out,” Lee said. Divers will inspect the reefs and point out certain areas that need more riprap, and cranes will lower rocks into certain places.

It’s important to have the 30-inch riprap on the outside of the reefs to create gaps between the rocks, Janssen said. Those crevices will attract crayfish, which in turn will attract hungry perch.

The UWM Water Institute plans to study the reef once it’s constructed to see if the fish like it, which will help them figure out ways to design better reefs in the future. That’ll take about five years, Janssen said.

In the first year, quagga mussels, which are a skinny version of a zebra mussels, will latch onto the rocks and begin filtering the water around the reefs. That’ll attract a thriving population of midges and amphipods that want to feed on the stuff growing on the rocks. Once the midge pupae hatch and begin riding their pupa case like a boat to the lake’s surface, the alewives and perch will come in to feed. Then, they’ll settle in and start spawning.

“We hope so,” Janssen said. “We don’t know until we check it out, and we have to check out why.”

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