Mississippi River faces triple threat: nitrates, salt, carp

On Jan. 21, the Star Tribune published an article that first appeared in the Milwaukee Journal Sentinel about the health of the Mississippi River, in particular, the Upper Mississippi River Basin, which includes Minnesota. Most of the article, however, focused on areas below the Minnesota border. With Earth Day just days away, many neighborhood organizations have planned cleanup operations, some of them directed at cleaning up the Mississippi River. That got us to thinking: Just how healthy is the river?

The Minnesota Pollution Control Agency (MPCA) 2024 Inventory of Impaired Waters lists several places along the river’s route from its headwaters at Lake Itasca to the Iowa border that are in not-so-good shape. The Mississippi, from Upper St. Anthony Falls to the St. Croix River, has been on the impaired list since 2008.

Nitrates from the north

The Mississippi Water Management Organization (MWMO) tests river water on a biweekly basis. The agency has jurisdiction over an intense 14-mile section of the river, from Islands of Peace in Fridley to Fort Snelling.

You may be surprised to learn that potatoes are the cause of much of the water pollution coming down from the north. From 2011-2015, R.D. Offutt Company, Fargo, N.D., bought nearly 8,000 acres of Minnesota’s forest lands from Potlatch Corp. Offutt is the largest single potato producer in the world, raising some 60,000 acres of irrigated potatoes in Minnesota, North Dakota, Wisconsin, Nebraska, Nevada, Oregon and Washington. One-third of Offutt’s U.S. potatoes are grown on nine farms in Minnesota.

The sandy soil in the area near Bemidji and Park Rapids is great for growing spuds. It’s also good at percolating the nitrates used to fertilize potatoes into area aquifers and streams, where the chemicals flow into the river.

Emily Resseger, research program manager at MWMO, said the river has been heavily impacted by upstream nitrates. “As potato farming has increased, we’ve seen more nitrates in the watershed, from Itasca on down,” she said. “We’re also beginning to get a handle on PFAs [“forever chemicals”].”

Salt in the metro

The most pervasive pollutant in the Twin Cities metro area is chloride – road salt. “It’s an urban pollutant, and and an emerging concern,” Resseger said.  

The MPCA and MWMO have worked with cities and the Minnesota Department of Transportation in the metro to spread “only as much salt as they need,” said MWMO Executive Director Kevin Reich. He said the “Smart Salting” program has had good acceptance among municipalities. (Lower salt use saves them money.)

Private companies are the next target for the program. Reich said property owners often worry about liabilities, so they salt their parking lots and driveways to excess. Changing that mindset will take time. “We [MWMO] don’t legislate,” he said. “We don’t offer sticks, just carrots. They need to feel like they’re doing the right thing.”

Invasive carp to the south

If you thought the 2015 closing of the Upper St. Anthony Lock and Dam protected Minneapolis from invasive carp, you’d be only partially correct. Carp are lurking in the Mississippi around Winona, 120 miles south of the Twin Cities. 

Colleen O’Connor Toberman, land use and planning program director for Friends of the Mississippi River (FMR) told people at a February meeting at Bottineau Park, “There are 175 miles below the St. Anthony Lock and Dam that are unprotected.”

Last December, the Minnesota Department of Natural Resources (DNR) removed a total of 408 invasive carp from Pool 6 of the Mississippi River near Trempealeau, Wis., the largest capture of invasive carp in Minnesota to date, according to Kelly Pennington, supervisor of the DNR’s Invasive Species Unit. In February, the DNR scooped up another 83 carp near Winona. 

Although non-native carp – grass, bighead, silver and black carp – are not yet reproducing in Minnesota waters, these habitat ruiners are hard to get rid of once they establish themselves. According to the DNR website, they were introduced to southern U.S. waters in the 1970s to control plants, algae and snails in fish farms, wastewater treatment and retention ponds. They escaped during high-water events and have been moving northward since. They’re voracious eaters and outcompete native fish for food. Silver carp are notorious for jumping ten feet out of water; some of these 25- to 40-lb. fish have hit boaters in the head.

FMR, along with fish biologist Dr. Peter Sorensen of the University of Minnesota, has been advocating for an emerging technology – a bioacoustic fish fence (BAFF) – installed at Lock and Dam 5 near Winona. A BAFF keeps fish away with sound and a curtain of air bubbles. They’re often used near hydroelectric dams; a BAFF has been used with some success at the Barkley Lock and Dam on the Cumberland River in Kentucky. Sorensen estimates a BAFF, along with other deterrent strategies, could keep 99% of invasive carp from traveling upstream; DNR’s Pennington says 50% is more likely.

Folks at FMR and the DNR are waiting to see what happens at the Minnesota Legislature this session. The Lessard-Sams Outdoor Heritage Council, which recommends spending from the state’s Outdoor Heritage Fund, has a $12 million windfall and could recommend, along with the DNR and the U.S. Fish & Wildlife Service, installation of a fish fence at Lock and Dam 5 near Winona.

Despite these threats, the river is “cleaner than it was when I was a kid in Northeast,” said MWMO’s Reich.  “We’re working to undo 100 years of unregulated industrial use in the watershed.”

What you can do to help the river

• If you fertilize your lawn or hire an application company to do it, make sure the granules are on the lawn and not on the sidewalk, where they can wash down the storm sewer.

• Similarly, keep grass clippings on your lawn. University of Minnesota Extension experts say decomposed clippings add the equivalent of one fertilizer application to your lawn each year. They also improve soil quality, minimize runoff and improve carbon sequestration.

• Plant native plants. They’ll suck up a lot of pollutants before they hit the river.

• Hook up a rain barrel to the gutters on your house and use the water on your outdoor plants. (House plants will love it, too!)

•  Keep storm sewers free of leaves, seeds and other materials. If you want to make a more formal commitment, sign up for Adopt-A-Drain: https://mn.adopt-a-drain.org/

• Join your neighbors in an Earth Day cleanup activity. If there isn’t one in your neighborhood, start one.

• In winter, use as little salt as possible – about a 12-oz. coffee cup full for every seven to ten sidewalk squares. Use sand for traction, sweep it up in the spring and reuse it next year.

• If you notice excessive salt use on the sidewalks and parking lots around your workplace, talk to your employer. Direct them to the
MPCA’s Smart Salting program: https://www.pca.state.mn.us/business-with-us/smart-salting-training.

• If you catch a nonnative carp, take its picture. Measure the length and weight, if possible. Send the photo and the location where you caught it to the DNR, 651-587-2781. They’ll authorize a permit that allows you to take the fish home and eat it; put the head and guts in a plastic bag and put them in the garbage – don’t toss them back into the river. If you see a flying silver carp, report it to https://www.eddmaps.org/ or email Grace.Loppnow@state.mn.us.