In just seven years, a ditch through an Allamakee County cornfield has been transformed into a tall-grass-prairie stream in which Iowa’s only native strain of trout flourishes.
Mike Osterholm, the landowner who orchestrated the transformation, calls it “a miracle in nature.”
“It is a testament to what Mother Nature can do with some help,” said Osterholm, 58, of Greenwood, Minn., whose vision, perseverance and bankroll helped nature reverse the tide of “progress” that has made Iowa the most-altered state in the nation.
Osterholm bought the property in 2002 from Ed Hahn, 69, of Dorchester, who recalls catching brook trout in the stream when he was a child growing up on the farm.
The stream, which originates in a spring gushing from a deep sandstone aquifer, was channeled in 1950 into a ditch and its tiny valley converted from native prairie into a cornfield.
Osterholm, a Luther College graduate with an affinity for northeast Iowa trout streams, used a 1949 aerial photo of the property to determine the precise location of the long-gone stream. Then, in 2004, he hired earth movers to re-create its original, meandering 1,280-foot course and replanted its banks with prairie cord grass and other native vegetation.
In the winter of 2007, Osterholm brought in 12 large truckloads of 2- to 4-inch rock to solidify the stream bed and reinforce the riffle-run pool pattern of a classic trout stream.
Osterholm isn’t sure how much he’s spent in total to restore the stream, but he does recall that the loads of rock alone cost him more than $10,000.
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In May 2009, the Department of Natural Resources stocked Brook Creek, as Osterholm christened it, with 500 fingerlings of the South Pine Creek strain of brook trout, the only native species to survive settlers’ disruption of the state’s original prairie.
A DNR census in June found “a bunch of 2-inch brookies that hatched from eggs deposited last fall by those stocked fish,” said DNR fisheries biologist Bill Kalishek.
In the fall, adult brook trout, many of them a foot long, were observed spawning on the stream’s several redds — rocky stream sections cleansed of silt by the fanning tails of pre-spawn female trout.
“That brings it full circle,” said Osterholm, who credits the DNR, the Natural Resources Conservation Service and several other partners for the stream’s complete and rapid transformation.
Kalishek said the Brook Creek population will help ensure the survival of the native brookies, which as recently as 15 years ago were known to exist only in South Pine — a tiny stream about 12 miles southwest of Osterholm’s Brook Creek.
“One accidental spill of anhydrous ammonia could wipe out the South Pine brookies,” he said.
Because Brook Creek’s small watershed is insulated from such potential disasters, it will provide a nearly fail-safe refuge for Iowa’s native brook trout strain, Kalishek said.
The stream’s greatest asset, Kalishek said, is its constant flow of cool, clear water. Because it issues from a deep aquifer, its output is hardly affected by heavy rains or droughts, and its temperature seldom varies from a range of 46 to 56 degrees Fahrenheit.
“That’s ideal for brook trout, but too cold for brown trout, which tend to out-compete brook trout in most Iowa streams,” Kalishek said.
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Osterholm said he has never seen ice on Brook Creek in the nearly 10 years he has owned the property.
The stream’s canopy of prairie grasses helps cool the stream in the summer, and the grasses’ extensive roots hold the banks in place, he said.
Osterholm said he is astounded by the explosion of plant and animal diversity that has accompanied the transformation.
Every species of frog known to inhabit Iowa has been found along the stream, and bird species visiting the valley have increased from about 40 to 150, he said.
The stream, he said, has proved to be “an insect factory,” with scientific samples recording 2,000 aquatic insects per square foot of stream surface. With such a surfeit of food, the trout are fat and happy, he said.
As much as Osterholm enjoys trout angling, he will not fish in Brook Creek, nor will anyone else.
The stream’s legacy will be as a refuge for the native brookies — available to the DNR as a stocking source for other streams and for milt and eggs for hatchery use, he said.