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The twisting stretch of the Pine River that runs more than 13 river miles from the U.S. Army Corps of Engineers dam in Crosslake to the Mississippi River in Crow Wing County is both remote and pristine.

Much of the meandering channel runs through public land and is shielded from development. Kayakers paddle in peace and quiet, free of motorboat or automobile noise. Fishermen chase after walleye and silver redhorses, also known as suckers, who in turn chase fish like the least darter, the smallest fish in Minnesota. The fish are easy to spot because the water is clear. The U.S. Forest Service has identified this watershed as the most important drainage basin for protecting clean drinking water for the Twin Cities.

“When you’re on this river, you only hear the river,” said Melissa Barrick, district manager of the Crow Wing Soil & Water Conservation District.

It’s almost perfect. Except, that is, for a crumbling rock dam.

The dam was put in a half-century ago to regulate water flow between Pine Lake and Pine River and to increase water levels in Pine Lake (also called Big Pine Lake).

It did its primary job — a slew of strategically placed boulders helped turn a wetland into a stable, shallow lake, creating valuable lakeshore real estate.

But the county-owned dam also became a decadeslong headache. Every few years seemed to bring major repairs, each time costing $15,000 to $20,000 without solving the problem. Over time, the dam grew, eventually expanding to twice its original size.

For many reasons — balancing the river’s ecology and aquatic health with the needs of lakeshore property owners and recreational users of the lake and river — the county needed a permanent solution before the patched-over dam fully failed. And that begins this month with the construction of a new rock riffle dam, which will create a series of rapids used to mimic the natural processes of the stream.

The new dam, funded by a $1.2 million grant from the state’s Outdoor Heritage Fund and slated to be completed this year, allows fish from the lower Pine and Mississippi rivers — walleye and redhorses and white suckers — to access good spawning habitat upstream, closer to the Crosslake Dam.

“It’s a win-win for us all,” said Tim Bray, the Crow Wing County engineer. “This is a permanent solution for not only keeping the water in the lake but also allowing fish passage.”

If the existing rock dam were to fully fail, the effects would be devastating, draining more than 400 acres of Pine Lake. A failed dam wouldn’t just mean disaster for lakeshore property owners; recreational boaters would be affected, as would fisheries and loon nesting habitat.

When the rock dam was originally built in 1970, a culvert was put in to aid fish passage upstream and past the rock dam. Over time, the culvert washed away because of high water flow. That meant fish habitats were affected. The most recent fish survey of the Pine River showed that the most sensitive species were declining, which is an indicator of what might be going on with other species.

“People will start noticing it when it’s too late and on the upper end of the food chain,” said Owen Baird, a fisheries management specialist in the Brainerd office of the Minnesota Department of Natural Resources.

“Humans have constricted fish movements and streams through culverts not sized or placed properly. We’ve fragmented habitats all over the place. Think of this dam like the circulatory system. When there’s lots of blood clots, blood still flows but not well. Clear it out and you can create overall health.”

Reid Forgrave • 612-673-4647