University of Wisconsin researchers have invented a new tool to control the invasive smelt population on inland waters: the Gradual Entrainment Lake Inverter (GELI).
Crystal Lake takes up an area of 100 acres and is 70 feet deep. Its clear, cold water is not only popular with campers and swimmers, but also with rainbow smelt — the “same exact species that is found up in Lake Superior,” according to UW graduate student Zach Lawson.
While anglers have learned to love the smelt in Lake Superior, Lawson said they have learned to hate them in Crystal Lake: “We see rainbow smelt consuming young of walleye, yellow perch, (and) whitefish,” he said.
The researchers came up with an idea to control the invasive smelt population: In the middle of summer, mixing the warm surface water of Crystal Lake with the cold water at the bottom.
“If you can mix those two layers, thereby warming that deep, cold water, then essentially you should be able to remove that cold water habitat that smelt need to survive,” said Lawson.
In order to mix the water in the 100-acre lake, Lawson helped invent the contraption known as the GELI.
“These things are basically like backyard trampolines,” he said. “They have a steel frame, about 30 feet in diameter. They sink in the water column, and we fill them with air and they rise to the surface. We oscillate that all day long, all summer long.”
Lawson said that after two years of mixing, the 45-degree bottom water had warmed to above 70 degrees, killing 90 percent of the smelt.
“90 percent is a lot, but it's not quite all of them,” said Lawson.
As the project wraps up this summer, Crystal Lake is being returned to it to its normal condition.